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 $216.84   3.459%   $224.3405   $224.34   $224.35   $224.30  
  Purchase #2 $249.25   11.278%   $277.3604   $277.36   $277.35   $277.40  
  Purchase #3 $64.73   4.692%   $67.7671   $67.77   $67.75   $67.80  
  Purchase #4 $37.66   12.528%   $42.378   $42.38   $42.40   $42.40  
  Purchase #5 $99.30   10.873%   $110.0969   $110.10   $110.10   $110.10  
  Purchase #6 $5.88   3.216%   $6.0691   $6.07   $6.05   $6.10  
  Purchase #7 $216.91   3.147%   $223.7362   $223.74   $223.75   $223.70  
  7 purchase totals = $890.57       $951.7482   $951.76   $951.75   $951.80