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 $90.66   13.185%   $102.6135   $102.61   $102.60   $102.60  
  Purchase #2 $176.75   10.581%   $195.4519   $195.45   $195.45   $195.50  
  Purchase #3 $234.43   11.743%   $261.9591   $261.96   $261.95   $262.00  
  Purchase #4 $32.32   13.196%   $36.5849   $36.58   $36.60   $36.60  
  Purchase #5 $112.98   9.307%   $123.495   $123.50   $123.50   $123.50  
  Purchase #6 $195.76   13.199%   $221.5984   $221.60   $221.60   $221.60  
  Purchase #7 $247.75   3.709%   $256.939   $256.94   $256.95   $256.90  
  7 purchase totals = $1,090.65       $1,198.6418   $1,198.64   $1,198.65   $1,198.70