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 $212.47   9.288%   $232.2042   $232.20   $232.20   $232.20  
  Purchase #2 $100.26   12.335%   $112.6271   $112.63   $112.65   $112.60  
  Purchase #3 $140.99   10.710%   $156.09   $156.09   $156.10   $156.10  
  Purchase #4 $146.54   10.403%   $161.7846   $161.78   $161.80   $161.80  
  Purchase #5 $178.42   7.651%   $192.0709   $192.07   $192.05   $192.10  
  Purchase #6 $85.61   12.476%   $96.2907   $96.29   $96.30   $96.30  
  Purchase #7 $121.38   3.345%   $125.4402   $125.44   $125.45   $125.40  
  7 purchase totals = $985.67       $1,076.5077   $1,076.50   $1,076.55   $1,076.50