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 $149.71   12.529%   $168.4672   $168.47   $168.45   $168.50  
  Purchase #2 $231.86   13.706%   $263.6387   $263.64   $263.65   $263.60  
  Purchase #3 $68.87   6.874%   $73.6041   $73.60   $73.60   $73.60  
  Purchase #4 $122.32   6.339%   $130.0739   $130.07   $130.05   $130.10  
  Purchase #5 $204.46   6.789%   $218.3408   $218.34   $218.35   $218.30  
  Purchase #6 $44.42   4.582%   $46.4553   $46.46   $46.45   $46.50  
  Purchase #7 $44.41   6.783%   $47.4223   $47.42   $47.40   $47.40  
  7 purchase totals = $866.05       $948.0023   $948.00   $947.95   $948.00