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 $234.48   9.612%   $257.0182   $257.02   $257.00   $257.00  
  Purchase #2 $54.71   13.756%   $62.2359   $62.24   $62.25   $62.20  
  Purchase #3 $119.81   9.657%   $131.3801   $131.38   $131.40   $131.40  
  Purchase #4 $220.65   12.539%   $248.3173   $248.32   $248.30   $248.30  
  Purchase #5 $85.26   6.609%   $90.8948   $90.89   $90.90   $90.90  
  Purchase #6 $82.60   6.752%   $88.1772   $88.18   $88.20   $88.20  
  Purchase #7 $211.68   13.872%   $241.0442   $241.04   $241.05   $241.00  
  7 purchase totals = $1,009.19       $1,119.0677   $1,119.07   $1,119.10   $1,119.00