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 $114.63   9.655%   $125.6975   $125.70   $125.70   $125.70  
  Purchase #2 $244.98   11.453%   $273.0376   $273.04   $273.05   $273.00  
  Purchase #3 $42.79   7.600%   $46.042   $46.04   $46.05   $46.00  
  Purchase #4 $185.66   8.155%   $200.8006   $200.80   $200.80   $200.80  
  Purchase #5 $27.78   10.743%   $30.7644   $30.76   $30.75   $30.80  
  Purchase #6 $72.39   3.279%   $74.7637   $74.76   $74.75   $74.80  
  Purchase #7 $69.55   3.803%   $72.195   $72.20   $72.20   $72.20  
  7 purchase totals = $757.78       $823.3008   $823.30   $823.30   $823.30