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 $96.69   8.360%   $104.7733   $104.77   $104.75   $104.80  
  Purchase #2 $69.33   6.774%   $74.0264   $74.03   $74.05   $74.00  
  Purchase #3 $180.34   9.732%   $197.8907   $197.89   $197.90   $197.90  
  Purchase #4 $104.92   11.664%   $117.1579   $117.16   $117.15   $117.20  
  Purchase #5 $185.35   10.383%   $204.5949   $204.59   $204.60   $204.60  
  Purchase #6 $94.69   10.323%   $104.4648   $104.46   $104.45   $104.50  
  Purchase #7 $68.70   7.343%   $73.7446   $73.74   $73.75   $73.70  
  7 purchase totals = $800.02       $876.6526   $876.64   $876.65   $876.70