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 $43.84   11.246%   $48.7702   $48.77   $48.75   $48.80  
  Purchase #2 $208.26   10.806%   $230.7646   $230.76   $230.75   $230.80  
  Purchase #3 $5.68   4.591%   $5.9408   $5.94   $5.95   $5.90  
  Purchase #4 $110.92   13.269%   $125.638   $125.64   $125.65   $125.60  
  Purchase #5 $65.42   12.811%   $73.801   $73.80   $73.80   $73.80  
  Purchase #6 $148.42   7.759%   $159.9359   $159.94   $159.95   $159.90  
  Purchase #7 $92.54   4.720%   $96.9079   $96.91   $96.90   $96.90  
  7 purchase totals = $675.08       $741.7584   $741.76   $741.75   $741.70