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 $60.78   4.821%   $63.7102   $63.71   $63.70   $63.70  
  Purchase #2 $33.38   5.214%   $35.1204   $35.12   $35.10   $35.10  
  Purchase #3 $250.59   9.201%   $273.6468   $273.65   $273.65   $273.60  
  Purchase #4 $200.91   10.227%   $221.4571   $221.46   $221.45   $221.50  
  Purchase #5 $152.87   3.763%   $158.6225   $158.62   $158.60   $158.60  
  Purchase #6 $89.99   3.397%   $93.047   $93.05   $93.05   $93.00  
  Purchase #7 $80.70   13.184%   $91.3395   $91.34   $91.35   $91.30  
  7 purchase totals = $869.22       $936.9435   $936.95   $936.90   $936.80