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 $206.76   12.713%   $233.0454   $233.05   $233.05   $233.00  
  Purchase #2 $148.71   9.511%   $162.8538   $162.85   $162.85   $162.90  
  Purchase #3 $233.32   5.410%   $245.9426   $245.94   $245.95   $245.90  
  Purchase #4 $145.50   8.865%   $158.3986   $158.40   $158.40   $158.40  
  Purchase #5 $81.63   4.761%   $85.5164   $85.52   $85.50   $85.50  
  Purchase #6 $126.52   7.602%   $136.1381   $136.14   $136.15   $136.10  
  Purchase #7 $173.91   11.175%   $193.3444   $193.34   $193.35   $193.30  
  7 purchase totals = $1,116.35       $1,215.2393   $1,215.24   $1,215.25   $1,215.10