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 $62.81   5.754%   $66.4241   $66.42   $66.40   $66.40  
  Purchase #2 $55.84   13.438%   $63.3438   $63.34   $63.35   $63.30  
  Purchase #3 $238.52   11.817%   $266.7059   $266.71   $266.70   $266.70  
  Purchase #4 $66.88   9.443%   $73.1955   $73.20   $73.20   $73.20  
  Purchase #5 $121.93   3.292%   $125.9439   $125.94   $125.95   $125.90  
  Purchase #6 $162.26   13.398%   $183.9996   $184.00   $184.00   $184.00  
  Purchase #7 $230.52   10.798%   $255.4115   $255.41   $255.40   $255.40  
  7 purchase totals = $938.76       $1,035.0243   $1,035.02   $1,035.00   $1,034.90