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 $233.94   5.420%   $246.6195   $246.62   $246.60   $246.60  
  Purchase #2 $167.70   3.477%   $173.5309   $173.53   $173.55   $173.50  
  Purchase #3 $152.71   12.123%   $171.223   $171.22   $171.20   $171.20  
  Purchase #4 $109.86   6.720%   $117.2426   $117.24   $117.25   $117.20  
  Purchase #5 $160.77   5.591%   $169.7587   $169.76   $169.75   $169.80  
  Purchase #6 $175.94   13.687%   $200.0209   $200.02   $200.00   $200.00  
  Purchase #7 $168.70   8.285%   $182.6768   $182.68   $182.70   $182.70  
  7 purchase totals = $1,169.62       $1,261.0724   $1,261.07   $1,261.05   $1,261.00