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 $58.33   3.545%   $60.3978   $60.40   $60.40   $60.40  
  Purchase #2 $173.47   5.272%   $182.6153   $182.62   $182.60   $182.60  
  Purchase #3 $129.53   7.159%   $138.8031   $138.80   $138.80   $138.80  
  Purchase #4 $47.50   7.207%   $50.9233   $50.92   $50.90   $50.90  
  Purchase #5 $222.61   6.454%   $236.9772   $236.98   $237.00   $237.00  
  Purchase #6 $92.99   11.233%   $103.4356   $103.44   $103.45   $103.40  
  Purchase #7 $237.72   5.526%   $250.8564   $250.86   $250.85   $250.90  
  7 purchase totals = $962.15       $1,024.0087   $1,024.02   $1,024.00   $1,024.00