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 $69.96   12.174%   $78.4769   $78.48   $78.50   $78.50  
  Purchase #2 $110.91   5.259%   $116.7428   $116.74   $116.75   $116.70  
  Purchase #3 $247.84   13.664%   $281.7049   $281.70   $281.70   $281.70  
  Purchase #4 $51.51   10.468%   $56.9021   $56.90   $56.90   $56.90  
  Purchase #5 $153.53   10.464%   $169.5954   $169.60   $169.60   $169.60  
  Purchase #6 $94.95   4.249%   $98.9844   $98.98   $99.00   $99.00  
  Purchase #7 $144.45   3.375%   $149.3252   $149.33   $149.35   $149.30  
  7 purchase totals = $873.15       $951.7317   $951.73   $951.80   $951.70