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 $209.65   6.716%   $223.7301   $223.73   $223.75   $223.70  
  Purchase #2 $84.95   11.683%   $94.8747   $94.87   $94.85   $94.90  
  Purchase #3 $67.84   8.138%   $73.3608   $73.36   $73.35   $73.40  
  Purchase #4 $163.62   13.438%   $185.6073   $185.61   $185.60   $185.60  
  Purchase #5 $165.75   9.844%   $182.0664   $182.07   $182.05   $182.10  
  Purchase #6 $30.84   3.555%   $31.9364   $31.94   $31.95   $31.90  
  Purchase #7 $123.93   7.677%   $133.4441   $133.44   $133.45   $133.40  
  7 purchase totals = $846.58       $925.0198   $925.02   $925.00   $925.00