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 $168.86   9.512%   $184.922   $184.92   $184.90   $184.90  
  Purchase #2 $125.68   11.570%   $140.2212   $140.22   $140.20   $140.20  
  Purchase #3 $238.36   13.859%   $271.3943   $271.39   $271.40   $271.40  
  Purchase #4 $142.54   10.180%   $157.0506   $157.05   $157.05   $157.10  
  Purchase #5 $248.35   7.246%   $266.3454   $266.35   $266.35   $266.30  
  Purchase #6 $234.97   13.289%   $266.1952   $266.20   $266.20   $266.20  
  Purchase #7 $77.31   3.869%   $80.3011   $80.30   $80.30   $80.30  
  7 purchase totals = $1,236.07       $1,366.4298   $1,366.43   $1,366.40   $1,366.40