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 $71.69   6.856%   $76.6051   $76.61   $76.60   $76.60  
  Purchase #2 $152.68   11.593%   $170.3802   $170.38   $170.40   $170.40  
  Purchase #3 $132.42   8.668%   $143.8982   $143.90   $143.90   $143.90  
  Purchase #4 $241.26   10.694%   $267.0603   $267.06   $267.05   $267.10  
  Purchase #5 $116.92   4.492%   $122.172   $122.17   $122.15   $122.20  
  Purchase #6 $42.27   8.649%   $45.9259   $45.93   $45.95   $45.90  
  Purchase #7 $233.61   9.248%   $255.2143   $255.21   $255.20   $255.20  
  7 purchase totals = $990.85       $1,081.2560   $1,081.26   $1,081.25   $1,081.30