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 $43.68   6.246%   $46.4083   $46.41   $46.40   $46.40  
  Purchase #2 $174.58   4.314%   $182.1114   $182.11   $182.10   $182.10  
  Purchase #3 $45.87   5.668%   $48.4699   $48.47   $48.45   $48.50  
  Purchase #4 $126.45   5.368%   $133.2378   $133.24   $133.25   $133.20  
  Purchase #5 $227.77   6.193%   $241.8758   $241.88   $241.90   $241.90  
  Purchase #6 $25.96   13.559%   $29.4799   $29.48   $29.50   $29.50  
  Purchase #7 $120.30   4.383%   $125.5727   $125.57   $125.55   $125.60  
  7 purchase totals = $764.61       $807.1558   $807.16   $807.15   $807.20