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 $69.44   11.532%   $77.4478   $77.45   $77.45   $77.40  
  Purchase #2 $239.89   10.787%   $265.7669   $265.77   $265.75   $265.80  
  Purchase #3 $111.65   5.308%   $117.5764   $117.58   $117.60   $117.60  
  Purchase #4 $215.66   4.811%   $226.0354   $226.04   $226.05   $226.00  
  Purchase #5 $167.84   3.420%   $173.5801   $173.58   $173.60   $173.60  
  Purchase #6 $166.55   7.684%   $179.3477   $179.35   $179.35   $179.30  
  Purchase #7 $233.73   9.462%   $255.8455   $255.85   $255.85   $255.80  
  7 purchase totals = $1,204.76       $1,295.5998   $1,295.62   $1,295.65   $1,295.50