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 $140.59   7.802%   $151.5588   $151.56   $151.55   $151.60  
  Purchase #2 $64.41   5.634%   $68.0389   $68.04   $68.05   $68.00  
  Purchase #3 $76.90   7.694%   $82.8167   $82.82   $82.80   $82.80  
  Purchase #4 $236.92   3.545%   $245.3188   $245.32   $245.30   $245.30  
  Purchase #5 $109.61   6.149%   $116.3499   $116.35   $116.35   $116.30  
  Purchase #6 $68.44   8.720%   $74.408   $74.41   $74.40   $74.40  
  Purchase #7 $190.47   12.699%   $214.6578   $214.66   $214.65   $214.70  
  7 purchase totals = $887.34       $953.1489   $953.16   $953.10   $953.10