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 $44.52   9.662%   $48.8215   $48.82   $48.80   $48.80  
  Purchase #2 $176.38   10.541%   $194.9722   $194.97   $194.95   $195.00  
  Purchase #3 $197.95   8.327%   $214.4333   $214.43   $214.45   $214.40  
  Purchase #4 $165.36   8.517%   $179.4437   $179.44   $179.45   $179.40  
  Purchase #5 $215.41   13.782%   $245.0978   $245.10   $245.10   $245.10  
  Purchase #6 $43.73   3.806%   $45.3944   $45.39   $45.40   $45.40  
  Purchase #7 $122.27   7.686%   $131.6677   $131.67   $131.65   $131.70  
  7 purchase totals = $965.62       $1,059.8306   $1,059.82   $1,059.80   $1,059.80