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 $115.25   8.456%   $124.9955   $125.00   $125.00   $125.00  
  Purchase #2 $179.63   6.805%   $191.8538   $191.85   $191.85   $191.90  
  Purchase #3 $151.28   4.171%   $157.5899   $157.59   $157.60   $157.60  
  Purchase #4 $13.71   5.343%   $14.4425   $14.44   $14.45   $14.40  
  Purchase #5 $239.39   3.394%   $247.5149   $247.51   $247.50   $247.50  
  Purchase #6 $244.36   5.671%   $258.2177   $258.22   $258.20   $258.20  
  Purchase #7 $11.91   6.639%   $12.7007   $12.70   $12.70   $12.70  
  7 purchase totals = $955.53       $1,007.3150   $1,007.31   $1,007.30   $1,007.30