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 $176.56   6.155%   $187.4273   $187.43   $187.45   $187.40  
  Purchase #2 $65.84   5.473%   $69.4434   $69.44   $69.45   $69.40  
  Purchase #3 $156.79   4.360%   $163.626   $163.63   $163.65   $163.60  
  Purchase #4 $213.84   8.680%   $232.4013   $232.40   $232.40   $232.40  
  Purchase #5 $205.50   5.731%   $217.2772   $217.28   $217.30   $217.30  
  Purchase #6 $66.67   9.457%   $72.975   $72.98   $73.00   $73.00  
  Purchase #7 $16.26   3.447%   $16.8205   $16.82   $16.80   $16.80  
  7 purchase totals = $901.46       $959.9707   $959.98   $960.05   $959.90