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 $196.48   13.817%   $223.6276   $223.63   $223.65   $223.60  
  Purchase #2 $59.27   10.691%   $65.6066   $65.61   $65.60   $65.60  
  Purchase #3 $68.32   7.153%   $73.2069   $73.21   $73.20   $73.20  
  Purchase #4 $244.92   12.181%   $274.7537   $274.75   $274.75   $274.80  
  Purchase #5 $117.63   7.703%   $126.691   $126.69   $126.70   $126.70  
  Purchase #6 $239.88   5.254%   $252.4833   $252.48   $252.50   $252.50  
  Purchase #7 $242.93   6.409%   $258.4994   $258.50   $258.50   $258.50  
  7 purchase totals = $1,169.43       $1,274.8685   $1,274.87   $1,274.90   $1,274.90