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 $61.61   11.485%   $68.6859   $68.69   $68.70   $68.70  
  Purchase #2 $137.81   6.456%   $146.707   $146.71   $146.70   $146.70  
  Purchase #3 $30.28   8.170%   $32.7539   $32.75   $32.75   $32.80  
  Purchase #4 $52.80   5.730%   $55.8254   $55.83   $55.85   $55.80  
  Purchase #5 $162.77   9.526%   $178.2755   $178.28   $178.30   $178.30  
  Purchase #6 $217.85   5.271%   $229.3329   $229.33   $229.35   $229.30  
  Purchase #7 $87.57   4.293%   $91.3294   $91.33   $91.35   $91.30  
  7 purchase totals = $750.69       $802.9100   $802.92   $803.00   $802.90