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 $248.83   8.347%   $269.5998   $269.60   $269.60   $269.60  
  Purchase #2 $89.29   10.156%   $98.3583   $98.36   $98.35   $98.40  
  Purchase #3 $230.33   9.627%   $252.5039   $252.50   $252.50   $252.50  
  Purchase #4 $213.96   5.174%   $225.0303   $225.03   $225.05   $225.00  
  Purchase #5 $158.25   9.339%   $173.029   $173.03   $173.05   $173.00  
  Purchase #6 $119.26   12.702%   $134.4084   $134.41   $134.40   $134.40  
  Purchase #7 $182.40   12.334%   $204.8972   $204.90   $204.90   $204.90  
  7 purchase totals = $1,242.32       $1,357.8269   $1,357.83   $1,357.85   $1,357.80