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 $246.69   6.345%   $262.3425   $262.34   $262.35   $262.30  
  Purchase #2 $83.26   11.627%   $92.9406   $92.94   $92.95   $92.90  
  Purchase #3 $40.91   13.605%   $46.4758   $46.48   $46.50   $46.50  
  Purchase #4 $224.97   13.125%   $254.4973   $254.50   $254.50   $254.50  
  Purchase #5 $185.83   8.734%   $202.0604   $202.06   $202.05   $202.10  
  Purchase #6 $176.56   11.761%   $197.3252   $197.33   $197.35   $197.30  
  Purchase #7 $161.29   6.478%   $171.7384   $171.74   $171.75   $171.70  
  7 purchase totals = $1,119.51       $1,227.3802   $1,227.39   $1,227.45   $1,227.30