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 $211.56   7.367%   $227.1456   $227.15   $227.15   $227.10  
  Purchase #2 $54.25   5.422%   $57.1914   $57.19   $57.20   $57.20  
  Purchase #3 $23.96   8.704%   $26.0455   $26.05   $26.05   $26.00  
  Purchase #4 $235.88   3.854%   $244.9708   $244.97   $244.95   $245.00  
  Purchase #5 $94.87   9.247%   $103.6426   $103.64   $103.65   $103.60  
  Purchase #6 $114.61   3.504%   $118.6259   $118.63   $118.65   $118.60  
  Purchase #7 $48.52   11.312%   $54.0086   $54.01   $54.00   $54.00  
  7 purchase totals = $783.65       $831.6304   $831.64   $831.65   $831.50