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 $61.50   11.417%   $68.5215   $68.52   $68.50   $68.50  
  Purchase #2 $20.96   11.619%   $23.3953   $23.40   $23.40   $23.40  
  Purchase #3 $48.49   12.471%   $54.5372   $54.54   $54.55   $54.50  
  Purchase #4 $204.38   4.694%   $213.9736   $213.97   $213.95   $214.00  
  Purchase #5 $78.95   6.481%   $84.0667   $84.07   $84.05   $84.10  
  Purchase #6 $242.25   4.120%   $252.2307   $252.23   $252.25   $252.20  
  Purchase #7 $158.34   8.584%   $171.9319   $171.93   $171.95   $171.90  
  7 purchase totals = $814.87       $868.6569   $868.66   $868.65   $868.60