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 $153.48   11.169%   $170.6222   $170.62   $170.60   $170.60  
  Purchase #2 $180.28   11.453%   $200.9275   $200.93   $200.95   $200.90  
  Purchase #3 $219.42   6.552%   $233.7964   $233.80   $233.80   $233.80  
  Purchase #4 $44.74   4.321%   $46.6732   $46.67   $46.65   $46.70  
  Purchase #5 $18.49   10.172%   $20.3708   $20.37   $20.35   $20.40  
  Purchase #6 $179.81   12.862%   $202.9372   $202.94   $202.95   $202.90  
  Purchase #7 $66.54   4.683%   $69.6561   $69.66   $69.65   $69.70  
  7 purchase totals = $862.76       $944.9834   $944.99   $944.95   $945.00