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 $182.89   12.228%   $205.2538   $205.25   $205.25   $205.30  
  Purchase #2 $93.82   7.589%   $100.94   $100.94   $100.95   $100.90  
  Purchase #3 $33.63   11.486%   $37.4927   $37.49   $37.50   $37.50  
  Purchase #4 $92.95   3.610%   $96.3055   $96.31   $96.30   $96.30  
  Purchase #5 $139.90   13.804%   $159.2118   $159.21   $159.20   $159.20  
  Purchase #6 $202.51   8.478%   $219.6788   $219.68   $219.70   $219.70  
  Purchase #7 $172.54   9.340%   $188.6552   $188.66   $188.65   $188.70  
  7 purchase totals = $918.24       $1,007.5378   $1,007.54   $1,007.55   $1,007.60