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 $76.94   12.664%   $86.6837   $86.68   $86.70   $86.70  
  Purchase #2 $48.52   4.252%   $50.5831   $50.58   $50.60   $50.60  
  Purchase #3 $117.85   12.473%   $132.5494   $132.55   $132.55   $132.50  
  Purchase #4 $142.49   5.249%   $149.9693   $149.97   $149.95   $150.00  
  Purchase #5 $33.85   5.389%   $35.6742   $35.67   $35.65   $35.70  
  Purchase #6 $215.27   6.404%   $229.0559   $229.06   $229.05   $229.10  
  Purchase #7 $200.73   3.721%   $208.1992   $208.20   $208.20   $208.20  
  7 purchase totals = $835.65       $892.7148   $892.71   $892.70   $892.80