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 $53.36   11.788%   $59.6501   $59.65   $59.65   $59.70  
  Purchase #2 $74.38   13.799%   $84.6437   $84.64   $84.65   $84.60  
  Purchase #3 $137.77   11.798%   $154.0241   $154.02   $154.00   $154.00  
  Purchase #4 $231.91   9.472%   $253.8765   $253.88   $253.90   $253.90  
  Purchase #5 $62.88   9.127%   $68.6191   $68.62   $68.60   $68.60  
  Purchase #6 $219.78   11.153%   $244.2921   $244.29   $244.30   $244.30  
  Purchase #7 $170.82   8.381%   $185.1364   $185.14   $185.15   $185.10  
  7 purchase totals = $950.90       $1,050.2420   $1,050.24   $1,050.25   $1,050.20