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 $55.66   13.698%   $63.2843   $63.28   $63.30   $63.30  
  Purchase #2 $95.89   10.826%   $106.2711   $106.27   $106.25   $106.30  
  Purchase #3 $205.99   3.178%   $212.5364   $212.54   $212.55   $212.50  
  Purchase #4 $14.55   5.674%   $15.3756   $15.38   $15.40   $15.40  
  Purchase #5 $54.55   9.736%   $59.861   $59.86   $59.85   $59.90  
  Purchase #6 $24.89   4.399%   $25.9849   $25.98   $26.00   $26.00  
  Purchase #7 $228.48   12.614%   $257.3005   $257.30   $257.30   $257.30  
  7 purchase totals = $680.01       $740.6138   $740.61   $740.65   $740.70