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 $129.57   3.684%   $134.3434   $134.34   $134.35   $134.30  
  Purchase #2 $222.96   11.659%   $248.9549   $248.95   $248.95   $249.00  
  Purchase #3 $123.35   7.251%   $132.2941   $132.29   $132.30   $132.30  
  Purchase #4 $42.51   9.776%   $46.6658   $46.67   $46.65   $46.70  
  Purchase #5 $205.81   3.287%   $212.575   $212.58   $212.60   $212.60  
  Purchase #6 $17.77   12.807%   $20.0458   $20.05   $20.05   $20.00  
  Purchase #7 $101.69   8.287%   $110.1171   $110.12   $110.10   $110.10  
  7 purchase totals = $843.66       $904.9961   $905.00   $905.00   $905.00