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 $85.25   9.257%   $93.1416   $93.14   $93.15   $93.10  
  Purchase #2 $189.77   13.190%   $214.8007   $214.80   $214.80   $214.80  
  Purchase #3 $96.40   13.715%   $109.6213   $109.62   $109.60   $109.60  
  Purchase #4 $77.48   10.672%   $85.7487   $85.75   $85.75   $85.70  
  Purchase #5 $190.28   10.654%   $210.5524   $210.55   $210.55   $210.60  
  Purchase #6 $187.71   5.157%   $197.3902   $197.39   $197.40   $197.40  
  Purchase #7 $22.63   4.555%   $23.6608   $23.66   $23.65   $23.70  
  7 purchase totals = $849.52       $934.9157   $934.91   $934.90   $934.90