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 $107.56   4.567%   $112.4723   $112.47   $112.45   $112.50  
  Purchase #2 $158.25   7.550%   $170.1979   $170.20   $170.20   $170.20  
  Purchase #3 $164.43   9.552%   $180.1364   $180.14   $180.15   $180.10  
  Purchase #4 $136.52   13.696%   $155.2178   $155.22   $155.20   $155.20  
  Purchase #5 $178.58   11.651%   $199.3864   $199.39   $199.40   $199.40  
  Purchase #6 $19.86   3.126%   $20.4808   $20.48   $20.50   $20.50  
  Purchase #7 $30.65   3.340%   $31.6737   $31.67   $31.65   $31.70  
  7 purchase totals = $795.85       $869.5653   $869.57   $869.55   $869.60