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 $59.27   3.328%   $61.2425   $61.24   $61.25   $61.20  
  Purchase #2 $240.38   8.650%   $261.1729   $261.17   $261.15   $261.20  
  Purchase #3 $82.31   12.146%   $92.3074   $92.31   $92.30   $92.30  
  Purchase #4 $67.42   9.145%   $73.5856   $73.59   $73.60   $73.60  
  Purchase #5 $209.79   12.470%   $235.9508   $235.95   $235.95   $236.00  
  Purchase #6 $186.42   8.122%   $201.561   $201.56   $201.55   $201.60  
  Purchase #7 $15.78   4.446%   $16.4816   $16.48   $16.50   $16.50  
  7 purchase totals = $861.37       $942.3018   $942.30   $942.30   $942.40