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 $201.69   10.142%   $222.1454   $222.15   $222.15   $222.10  
  Purchase #2 $111.48   4.192%   $116.1532   $116.15   $116.15   $116.20  
  Purchase #3 $46.83   5.832%   $49.5611   $49.56   $49.55   $49.60  
  Purchase #4 $207.95   8.817%   $226.285   $226.29   $226.30   $226.30  
  Purchase #5 $148.50   7.667%   $159.8855   $159.89   $159.90   $159.90  
  Purchase #6 $228.96   4.564%   $239.4097   $239.41   $239.40   $239.40  
  Purchase #7 $204.53   10.443%   $225.8891   $225.89   $225.90   $225.90  
  7 purchase totals = $1,149.94       $1,239.3290   $1,239.34   $1,239.35   $1,239.40