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   13.196%   $96.4996   $96.50   $96.50   $96.50  
  Purchase #2 $53.46   9.338%   $58.4521   $58.45   $58.45   $58.50  
  Purchase #3 $118.56   12.350%   $133.2022   $133.20   $133.20   $133.20  
  Purchase #4 $167.44   6.288%   $177.9686   $177.97   $177.95   $178.00  
  Purchase #5 $168.82   11.610%   $188.42   $188.42   $188.40   $188.40  
  Purchase #6 $5.73   12.535%   $6.4483   $6.45   $6.45   $6.40  
  Purchase #7 $250.54   7.567%   $269.4984   $269.50   $269.50   $269.50  
  7 purchase totals = $849.80       $930.4892   $930.49   $930.45   $930.50