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 $63.95   4.686%   $66.9467   $66.95   $66.95   $66.90  
  Purchase #2 $226.71   12.206%   $254.3822   $254.38   $254.40   $254.40  
  Purchase #3 $204.33   7.164%   $218.9682   $218.97   $218.95   $219.00  
  Purchase #4 $37.73   4.315%   $39.358   $39.36   $39.35   $39.40  
  Purchase #5 $199.71   3.682%   $207.0633   $207.06   $207.05   $207.10  
  Purchase #6 $133.35   13.375%   $151.1856   $151.19   $151.20   $151.20  
  Purchase #7 $27.92   10.225%   $30.7748   $30.77   $30.75   $30.80  
  7 purchase totals = $893.70       $968.6788   $968.68   $968.65   $968.80