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 $224.62   11.772%   $251.0623   $251.06   $251.05   $251.10  
  Purchase #2 $133.48   13.373%   $151.3303   $151.33   $151.35   $151.30  
  Purchase #3 $100.39   3.834%   $104.239   $104.24   $104.25   $104.20  
  Purchase #4 $166.93   11.664%   $186.4007   $186.40   $186.40   $186.40  
  Purchase #5 $91.47   7.171%   $98.0293   $98.03   $98.05   $98.00  
  Purchase #6 $167.88   4.122%   $174.8   $174.80   $174.80   $174.80  
  Purchase #7 $247.87   4.202%   $258.2855   $258.29   $258.30   $258.30  
  7 purchase totals = $1,132.64       $1,224.1471   $1,224.15   $1,224.20   $1,224.10