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 $208.65   8.321%   $226.0118   $226.01   $226.00   $226.00  
  Purchase #2 $93.39   3.220%   $96.3972   $96.40   $96.40   $96.40  
  Purchase #3 $102.63   7.472%   $110.2985   $110.30   $110.30   $110.30  
  Purchase #4 $22.42   6.597%   $23.899   $23.90   $23.90   $23.90  
  Purchase #5 $30.77   11.354%   $34.2636   $34.26   $34.25   $34.30  
  Purchase #6 $151.27   10.172%   $166.6572   $166.66   $166.65   $166.70  
  Purchase #7 $206.85   7.339%   $222.0307   $222.03   $222.05   $222.00  
  7 purchase totals = $815.98       $879.5580   $879.56   $879.55   $879.60