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 $233.65   12.799%   $263.5549   $263.55   $263.55   $263.60  
  Purchase #2 $181.89   8.656%   $197.6344   $197.63   $197.65   $197.60  
  Purchase #3 $34.40   6.306%   $36.5693   $36.57   $36.55   $36.60  
  Purchase #4 $162.94   12.706%   $183.6432   $183.64   $183.65   $183.60  
  Purchase #5 $116.87   9.201%   $127.6232   $127.62   $127.60   $127.60  
  Purchase #6 $178.32   12.169%   $200.0198   $200.02   $200.00   $200.00  
  Purchase #7 $176.45   4.852%   $185.0114   $185.01   $185.00   $185.00  
  7 purchase totals = $1,084.52       $1,194.0562   $1,194.04   $1,194.00   $1,194.00