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 $65.34   12.766%   $73.6813   $73.68   $73.70   $73.70  
  Purchase #2 $219.73   12.726%   $247.6928   $247.69   $247.70   $247.70  
  Purchase #3 $165.55   3.350%   $171.0959   $171.10   $171.10   $171.10  
  Purchase #4 $39.38   8.197%   $42.608   $42.61   $42.60   $42.60  
  Purchase #5 $51.86   7.815%   $55.9129   $55.91   $55.90   $55.90  
  Purchase #6 $150.54   8.493%   $163.3254   $163.33   $163.35   $163.30  
  Purchase #7 $5.73   11.767%   $6.4042   $6.40   $6.40   $6.40  
  7 purchase totals = $698.13       $760.7205   $760.72   $760.75   $760.70