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 $66.29   11.646%   $74.0101   $74.01   $74.00   $74.00  
  Purchase #2 $138.82   8.701%   $150.8987   $150.90   $150.90   $150.90  
  Purchase #3 $195.65   11.297%   $217.7526   $217.75   $217.75   $217.80  
  Purchase #4 $149.34   5.420%   $157.4342   $157.43   $157.45   $157.40  
  Purchase #5 $168.62   6.122%   $178.9429   $178.94   $178.95   $178.90  
  Purchase #6 $94.33   8.738%   $102.5726   $102.57   $102.55   $102.60  
  Purchase #7 $61.54   10.584%   $68.0534   $68.05   $68.05   $68.10  
  7 purchase totals = $874.59       $949.6645   $949.65   $949.65   $949.70