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 $5.92   13.465%   $6.7171   $6.72   $6.70   $6.70  
  Purchase #2 $71.66   4.139%   $74.626   $74.63   $74.65   $74.60  
  Purchase #3 $221.78   9.349%   $242.5142   $242.51   $242.50   $242.50  
  Purchase #4 $102.37   12.292%   $114.9533   $114.95   $114.95   $115.00  
  Purchase #5 $216.73   10.317%   $239.09   $239.09   $239.10   $239.10  
  Purchase #6 $164.90   4.671%   $172.6025   $172.60   $172.60   $172.60  
  Purchase #7 $93.46   9.719%   $102.5434   $102.54   $102.55   $102.50  
  7 purchase totals = $876.82       $953.0465   $953.04   $953.05   $953.00