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 $64.93   12.391%   $72.9755   $72.98   $73.00   $73.00  
  Purchase #2 $227.77   7.132%   $244.0146   $244.01   $244.00   $244.00  
  Purchase #3 $89.70   5.501%   $94.6344   $94.63   $94.65   $94.60  
  Purchase #4 $32.76   10.418%   $36.1729   $36.17   $36.15   $36.20  
  Purchase #5 $60.43   10.697%   $66.8942   $66.89   $66.90   $66.90  
  Purchase #6 $236.93   5.783%   $250.6317   $250.63   $250.65   $250.60  
  Purchase #7 $196.48   7.496%   $211.2081   $211.21   $211.20   $211.20  
  7 purchase totals = $909.00       $976.5314   $976.52   $976.55   $976.50