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 $106.53   12.167%   $119.4915   $119.49   $119.50   $119.50  
  Purchase #2 $162.86   12.738%   $183.6051   $183.61   $183.60   $183.60  
  Purchase #3 $186.47   10.709%   $206.4391   $206.44   $206.45   $206.40  
  Purchase #4 $93.90   7.829%   $101.2514   $101.25   $101.25   $101.30  
  Purchase #5 $9.99   6.168%   $10.6062   $10.61   $10.60   $10.60  
  Purchase #6 $105.85   9.305%   $115.6993   $115.70   $115.70   $115.70  
  Purchase #7 $181.66   4.521%   $189.8728   $189.87   $189.85   $189.90  
  7 purchase totals = $847.26       $926.9654   $926.97   $926.95   $927.00