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 $58.81   10.268%   $64.8486   $64.85   $64.85   $64.80  
  Purchase #2 $230.45   4.530%   $240.8894   $240.89   $240.90   $240.90  
  Purchase #3 $115.36   4.557%   $120.617   $120.62   $120.60   $120.60  
  Purchase #4 $176.89   3.140%   $182.4443   $182.44   $182.45   $182.40  
  Purchase #5 $183.54   3.422%   $189.8207   $189.82   $189.80   $189.80  
  Purchase #6 $73.34   10.375%   $80.949   $80.95   $80.95   $80.90  
  Purchase #7 $8.27   4.314%   $8.6268   $8.63   $8.65   $8.60  
  7 purchase totals = $846.66       $888.1958   $888.20   $888.20   $888.00