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 $211.58   7.425%   $227.2898   $227.29   $227.30   $227.30  
  Purchase #2 $103.49   12.142%   $116.0558   $116.06   $116.05   $116.10  
  Purchase #3 $157.35   6.832%   $168.1002   $168.10   $168.10   $168.10  
  Purchase #4 $187.49   6.643%   $199.945   $199.95   $199.95   $199.90  
  Purchase #5 $57.33   13.106%   $64.8437   $64.84   $64.85   $64.80  
  Purchase #6 $66.70   10.777%   $73.8883   $73.89   $73.90   $73.90  
  Purchase #7 $107.70   3.516%   $111.4867   $111.49   $111.50   $111.50  
  7 purchase totals = $891.64       $961.6095   $961.62   $961.65   $961.60