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 $40.82   6.587%   $43.5088   $43.51   $43.50   $43.50  
  Purchase #2 $234.79   13.689%   $266.9304   $266.93   $266.95   $266.90  
  Purchase #3 $89.85   9.117%   $98.0416   $98.04   $98.05   $98.00  
  Purchase #4 $81.90   8.373%   $88.7575   $88.76   $88.75   $88.80  
  Purchase #5 $9.60   13.264%   $10.8733   $10.87   $10.85   $10.90  
  Purchase #6 $133.58   9.408%   $146.1472   $146.15   $146.15   $146.10  
  Purchase #7 $244.90   7.271%   $262.7067   $262.71   $262.70   $262.70  
  7 purchase totals = $835.44       $916.9655   $916.97   $916.95   $916.90