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 $24.76   3.642%   $25.6618   $25.66   $25.65   $25.70  
  Purchase #2 $94.27   6.534%   $100.4296   $100.43   $100.45   $100.40  
  Purchase #3 $49.85   3.675%   $51.682   $51.68   $51.70   $51.70  
  Purchase #4 $158.86   4.199%   $165.5305   $165.53   $165.55   $165.50  
  Purchase #5 $92.72   5.858%   $98.1515   $98.15   $98.15   $98.20  
  Purchase #6 $53.97   7.311%   $57.9157   $57.92   $57.90   $57.90  
  Purchase #7 $226.65   7.688%   $244.0749   $244.07   $244.05   $244.10  
  7 purchase totals = $701.08       $743.4460   $743.44   $743.45   $743.50