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 $34.69   3.844%   $36.0235   $36.02   $36.00   $36.00  
  Purchase #2 $71.31   6.539%   $75.973   $75.97   $75.95   $76.00  
  Purchase #3 $129.95   6.433%   $138.3097   $138.31   $138.30   $138.30  
  Purchase #4 $133.95   13.218%   $151.6555   $151.66   $151.65   $151.70  
  Purchase #5 $124.68   11.799%   $139.391   $139.39   $139.40   $139.40  
  Purchase #6 $207.67   8.480%   $225.2804   $225.28   $225.30   $225.30  
  Purchase #7 $179.76   6.103%   $190.7308   $190.73   $190.75   $190.70  
  7 purchase totals = $882.01       $957.3639   $957.36   $957.35   $957.40