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 $244.91   13.491%   $277.9508   $277.95   $277.95   $278.00  
  Purchase #2 $157.45   4.646%   $164.7651   $164.77   $164.75   $164.80  
  Purchase #3 $101.36   10.454%   $111.9562   $111.96   $111.95   $112.00  
  Purchase #4 $226.56   11.761%   $253.2057   $253.21   $253.20   $253.20  
  Purchase #5 $23.54   7.837%   $25.3848   $25.38   $25.40   $25.40  
  Purchase #6 $167.33   13.566%   $190.03   $190.03   $190.05   $190.00  
  Purchase #7 $184.50   5.107%   $193.9224   $193.92   $193.90   $193.90  
  7 purchase totals = $1,105.65       $1,217.2150   $1,217.22   $1,217.20   $1,217.30