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 $244.98   6.557%   $261.0433   $261.04   $261.05   $261.00  
  Purchase #2 $121.65   8.749%   $132.2932   $132.29   $132.30   $132.30  
  Purchase #3 $140.62   9.639%   $154.1744   $154.17   $154.15   $154.20  
  Purchase #4 $102.44   12.499%   $115.244   $115.24   $115.25   $115.20  
  Purchase #5 $196.33   8.459%   $212.9376   $212.94   $212.95   $212.90  
  Purchase #6 $243.97   10.468%   $269.5088   $269.51   $269.50   $269.50  
  Purchase #7 $74.89   6.717%   $79.9204   $79.92   $79.90   $79.90  
  7 purchase totals = $1,124.88       $1,225.1217   $1,225.11   $1,225.10   $1,225.00