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 $127.90   3.664%   $132.5863   $132.59   $132.60   $132.60  
  Purchase #2 $233.88   12.430%   $262.9513   $262.95   $262.95   $263.00  
  Purchase #3 $15.49   3.731%   $16.0679   $16.07   $16.05   $16.10  
  Purchase #4 $46.96   11.313%   $52.2726   $52.27   $52.25   $52.30  
  Purchase #5 $199.87   3.809%   $207.483   $207.48   $207.50   $207.50  
  Purchase #6 $173.49   5.413%   $182.881   $182.88   $182.90   $182.90  
  Purchase #7 $128.79   7.529%   $138.4866   $138.49   $138.50   $138.50  
  7 purchase totals = $926.38       $992.7287   $992.73   $992.75   $992.90