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 $69.67   3.619%   $72.1914   $72.19   $72.20   $72.20  
  Purchase #2 $232.37   11.461%   $259.0019   $259.00   $259.00   $259.00  
  Purchase #3 $78.49   10.784%   $86.9544   $86.95   $86.95   $87.00  
  Purchase #4 $109.72   8.781%   $119.3545   $119.35   $119.35   $119.40  
  Purchase #5 $104.86   6.838%   $112.0303   $112.03   $112.05   $112.00  
  Purchase #6 $226.67   6.744%   $241.9566   $241.96   $241.95   $242.00  
  Purchase #7 $135.76   9.258%   $148.3287   $148.33   $148.35   $148.30  
  7 purchase totals = $957.54       $1,039.8178   $1,039.81   $1,039.85   $1,039.90