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 $88.80   6.234%   $94.3358   $94.34   $94.35   $94.30  
  Purchase #2 $185.75   6.193%   $197.2535   $197.25   $197.25   $197.30  
  Purchase #3 $50.34   8.786%   $54.7629   $54.76   $54.75   $54.80  
  Purchase #4 $5.35   9.442%   $5.8551   $5.86   $5.85   $5.90  
  Purchase #5 $97.75   7.297%   $104.8828   $104.88   $104.90   $104.90  
  Purchase #6 $118.48   6.269%   $125.9075   $125.91   $125.90   $125.90  
  Purchase #7 $194.59   6.309%   $206.8667   $206.87   $206.85   $206.90  
  7 purchase totals = $741.06       $789.8643   $789.87   $789.85   $790.00