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 $204.41   13.618%   $232.2466   $232.25   $232.25   $232.20  
  Purchase #2 $89.41   5.858%   $94.6476   $94.65   $94.65   $94.60  
  Purchase #3 $104.35   12.109%   $116.9857   $116.99   $117.00   $117.00  
  Purchase #4 $164.80   8.773%   $179.2579   $179.26   $179.25   $179.30  
  Purchase #5 $151.32   4.377%   $157.9433   $157.94   $157.95   $157.90  
  Purchase #6 $51.87   8.237%   $56.1425   $56.14   $56.15   $56.10  
  Purchase #7 $100.66   9.125%   $109.8452   $109.85   $109.85   $109.80  
  7 purchase totals = $866.82       $947.0688   $947.08   $947.10   $946.90