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 $93.56   3.857%   $97.1686   $97.17   $97.15   $97.20  
  Purchase #2 $44.27   8.255%   $47.9245   $47.92   $47.90   $47.90  
  Purchase #3 $42.82   12.475%   $48.1618   $48.16   $48.15   $48.20  
  Purchase #4 $218.62   12.144%   $245.1692   $245.17   $245.15   $245.20  
  Purchase #5 $195.33   13.433%   $221.5687   $221.57   $221.55   $221.60  
  Purchase #6 $229.87   9.651%   $252.0548   $252.05   $252.05   $252.10  
  Purchase #7 $96.49   3.777%   $100.1344   $100.13   $100.15   $100.10  
  7 purchase totals = $920.96       $1,012.1820   $1,012.17   $1,012.10   $1,012.30