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 $226.63   11.849%   $253.4834   $253.48   $253.50   $253.50  
  Purchase #2 $43.94   6.639%   $46.8572   $46.86   $46.85   $46.90  
  Purchase #3 $212.31   10.168%   $233.8977   $233.90   $233.90   $233.90  
  Purchase #4 $197.75   6.701%   $211.0012   $211.00   $211.00   $211.00  
  Purchase #5 $157.27   3.185%   $162.279   $162.28   $162.30   $162.30  
  Purchase #6 $181.63   7.136%   $194.5911   $194.59   $194.60   $194.60  
  Purchase #7 $53.94   13.189%   $61.0541   $61.05   $61.05   $61.10  
  7 purchase totals = $1,073.47       $1,163.1637   $1,163.16   $1,163.20   $1,163.30