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 $62.80   6.713%   $67.0158   $67.02   $67.00   $67.00  
  Purchase #2 $27.46   12.290%   $30.8348   $30.83   $30.85   $30.80  
  Purchase #3 $43.48   10.237%   $47.931   $47.93   $47.95   $47.90  
  Purchase #4 $55.36   12.162%   $62.0929   $62.09   $62.10   $62.10  
  Purchase #5 $242.43   6.729%   $258.7431   $258.74   $258.75   $258.70  
  Purchase #6 $113.37   5.451%   $119.5498   $119.55   $119.55   $119.50  
  Purchase #7 $162.91   7.145%   $174.5499   $174.55   $174.55   $174.50  
  7 purchase totals = $707.81       $760.7173   $760.71   $760.75   $760.50