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 $243.61   9.707%   $267.2572   $267.26   $267.25   $267.30  
  Purchase #2 $126.34   10.526%   $139.6385   $139.64   $139.65   $139.60  
  Purchase #3 $197.76   13.420%   $224.2994   $224.30   $224.30   $224.30  
  Purchase #4 $249.86   7.507%   $268.617   $268.62   $268.60   $268.60  
  Purchase #5 $238.88   3.291%   $246.7415   $246.74   $246.75   $246.70  
  Purchase #6 $77.76   6.261%   $82.6286   $82.63   $82.65   $82.60  
  Purchase #7 $110.27   12.432%   $123.9788   $123.98   $124.00   $124.00  
  7 purchase totals = $1,244.48       $1,353.1610   $1,353.17   $1,353.20   $1,353.10