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 $98.92   3.836%   $102.7146   $102.71   $102.70   $102.70  
  Purchase #2 $126.62   11.485%   $141.1623   $141.16   $141.15   $141.20  
  Purchase #3 $49.29   12.848%   $55.6228   $55.62   $55.60   $55.60  
  Purchase #4 $232.85   5.181%   $244.914   $244.91   $244.90   $244.90  
  Purchase #5 $6.41   13.432%   $7.271   $7.27   $7.25   $7.30  
  Purchase #6 $119.53   10.109%   $131.6133   $131.61   $131.60   $131.60  
  Purchase #7 $177.37   6.744%   $189.3318   $189.33   $189.35   $189.30  
  7 purchase totals = $810.99       $872.6298   $872.61   $872.55   $872.60