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 $55.91   9.463%   $61.2008   $61.20   $61.20   $61.20  
  Purchase #2 $179.47   11.219%   $199.6047   $199.60   $199.60   $199.60  
  Purchase #3 $84.71   9.303%   $92.5906   $92.59   $92.60   $92.60  
  Purchase #4 $140.53   4.142%   $146.3508   $146.35   $146.35   $146.40  
  Purchase #5 $127.53   11.679%   $142.4242   $142.42   $142.40   $142.40  
  Purchase #6 $186.37   4.828%   $195.3679   $195.37   $195.35   $195.40  
  Purchase #7 $127.57   5.804%   $134.9742   $134.97   $134.95   $135.00  
  7 purchase totals = $902.09       $972.5132   $972.50   $972.45   $972.60