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 $209.92   6.826%   $224.2491   $224.25   $224.25   $224.20  
  Purchase #2 $140.48   7.459%   $150.9584   $150.96   $150.95   $151.00  
  Purchase #3 $227.33   7.762%   $244.9754   $244.98   $245.00   $245.00  
  Purchase #4 $167.62   9.622%   $183.7484   $183.75   $183.75   $183.70  
  Purchase #5 $174.87   4.133%   $182.0974   $182.10   $182.10   $182.10  
  Purchase #6 $229.55   5.488%   $242.1477   $242.15   $242.15   $242.10  
  Purchase #7 $217.48   8.243%   $235.4069   $235.41   $235.40   $235.40  
  7 purchase totals = $1,367.25       $1,463.5833   $1,463.60   $1,463.60   $1,463.50