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 $188.93   3.521%   $195.5822   $195.58   $195.60   $195.60  
  Purchase #2 $22.92   10.783%   $25.3915   $25.39   $25.40   $25.40  
  Purchase #3 $167.57   8.788%   $182.2961   $182.30   $182.30   $182.30  
  Purchase #4 $235.47   4.429%   $245.899   $245.90   $245.90   $245.90  
  Purchase #5 $46.67   9.518%   $51.1121   $51.11   $51.10   $51.10  
  Purchase #6 $21.46   5.494%   $22.639   $22.64   $22.65   $22.60  
  Purchase #7 $116.71   5.609%   $123.2563   $123.26   $123.25   $123.30  
  7 purchase totals = $799.73       $846.1762   $846.18   $846.20   $846.20