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 $10.56   5.642%   $11.1558   $11.16   $11.15   $11.20  
  Purchase #2 $234.57   7.136%   $251.3089   $251.31   $251.30   $251.30  
  Purchase #3 $179.93   4.747%   $188.4713   $188.47   $188.45   $188.50  
  Purchase #4 $34.59   10.733%   $38.3025   $38.30   $38.30   $38.30  
  Purchase #5 $203.62   6.774%   $217.4132   $217.41   $217.40   $217.40  
  Purchase #6 $100.82   11.291%   $112.2036   $112.20   $112.20   $112.20  
  Purchase #7 $197.48   9.165%   $215.579   $215.58   $215.60   $215.60  
  7 purchase totals = $961.57       $1,034.4343   $1,034.43   $1,034.40   $1,034.50