Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $197.25   13.786%   $224.4429   $224.44   $224.45   $224.40  
  Purchase #2 $138.79   10.811%   $153.7946   $153.79   $153.80   $153.80  
  Purchase #3 $220.99   11.344%   $246.0591   $246.06   $246.05   $246.10  
  Purchase #4 $127.87   10.649%   $141.4869   $141.49   $141.50   $141.50  
  Purchase #5 $180.99   12.340%   $203.3242   $203.32   $203.30   $203.30  
  Purchase #6 $161.25   7.465%   $173.2873   $173.29   $173.30   $173.30  
  Purchase #7 $114.94   7.323%   $123.3571   $123.36   $123.35   $123.40  
  7 purchase totals = $1,142.08       $1,265.7521   $1,265.75   $1,265.75   $1,265.80