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 $59.59   12.348%   $66.9482   $66.95   $66.95   $66.90  
  Purchase #2 $111.95   12.808%   $126.2886   $126.29   $126.30   $126.30  
  Purchase #3 $134.70   13.708%   $153.1647   $153.16   $153.15   $153.20  
  Purchase #4 $183.50   13.211%   $207.7422   $207.74   $207.75   $207.70  
  Purchase #5 $216.87   12.194%   $243.3151   $243.32   $243.30   $243.30  
  Purchase #6 $186.28   13.114%   $210.7088   $210.71   $210.70   $210.70  
  Purchase #7 $117.86   5.246%   $124.0429   $124.04   $124.05   $124.00  
  7 purchase totals = $1,010.75       $1,132.2105   $1,132.21   $1,132.20   $1,132.10