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 $168.81   10.495%   $186.5266   $186.53   $186.55   $186.50  
  Purchase #2 $70.30   8.755%   $76.4548   $76.45   $76.45   $76.50  
  Purchase #3 $81.76   7.530%   $87.9165   $87.92   $87.90   $87.90  
  Purchase #4 $46.74   5.534%   $49.3266   $49.33   $49.35   $49.30  
  Purchase #5 $207.53   10.577%   $229.4804   $229.48   $229.50   $229.50  
  Purchase #6 $227.83   7.365%   $244.6097   $244.61   $244.60   $244.60  
  Purchase #7 $92.28   9.407%   $100.9608   $100.96   $100.95   $101.00  
  7 purchase totals = $895.25       $975.2754   $975.28   $975.30   $975.30