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 $240.87   8.784%   $262.028   $262.03   $262.05   $262.00  
  Purchase #2 $242.78   13.178%   $274.7735   $274.77   $274.75   $274.80  
  Purchase #3 $131.55   11.191%   $146.2718   $146.27   $146.25   $146.30  
  Purchase #4 $149.68   7.654%   $161.1365   $161.14   $161.15   $161.10  
  Purchase #5 $222.89   9.167%   $243.3223   $243.32   $243.30   $243.30  
  Purchase #6 $117.99   3.507%   $122.1279   $122.13   $122.15   $122.10  
  Purchase #7 $169.80   12.609%   $191.2101   $191.21   $191.20   $191.20  
  7 purchase totals = $1,275.56       $1,400.8701   $1,400.87   $1,400.85   $1,400.80