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 $63.67   7.545%   $68.4739   $68.47   $68.45   $68.50  
  Purchase #2 $173.44   5.239%   $182.5265   $182.53   $182.55   $182.50  
  Purchase #3 $59.32   7.296%   $63.648   $63.65   $63.65   $63.60  
  Purchase #4 $152.53   9.433%   $166.9182   $166.92   $166.90   $166.90  
  Purchase #5 $159.32   5.631%   $168.2913   $168.29   $168.30   $168.30  
  Purchase #6 $110.84   10.750%   $122.7553   $122.76   $122.75   $122.80  
  Purchase #7 $19.98   7.116%   $21.4018   $21.40   $21.40   $21.40  
  7 purchase totals = $739.10       $794.0150   $794.02   $794.00   $794.00