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 $58.46   9.178%   $63.8255   $63.83   $63.85   $63.80  
  Purchase #2 $69.38   6.525%   $73.907   $73.91   $73.90   $73.90  
  Purchase #3 $68.74   7.168%   $73.6673   $73.67   $73.65   $73.70  
  Purchase #4 $183.29   11.468%   $204.3097   $204.31   $204.30   $204.30  
  Purchase #5 $61.43   3.238%   $63.4191   $63.42   $63.40   $63.40  
  Purchase #6 $110.69   6.451%   $117.8306   $117.83   $117.85   $117.80  
  Purchase #7 $110.92   12.788%   $125.1044   $125.10   $125.10   $125.10  
  7 purchase totals = $662.91       $722.0636   $722.07   $722.05   $722.00