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 $95.53   3.456%   $98.8315   $98.83   $98.85   $98.80  
  Purchase #2 $105.36   13.836%   $119.9376   $119.94   $119.95   $119.90  
  Purchase #3 $6.73   7.719%   $7.2495   $7.25   $7.25   $7.20  
  Purchase #4 $51.33   6.626%   $54.7311   $54.73   $54.75   $54.70  
  Purchase #5 $191.49   5.763%   $202.5256   $202.53   $202.55   $202.50  
  Purchase #6 $11.65   6.638%   $12.4233   $12.42   $12.40   $12.40  
  Purchase #7 $203.32   6.836%   $217.219   $217.22   $217.20   $217.20  
  7 purchase totals = $665.41       $712.9176   $712.92   $712.95   $712.70