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 $240.26   10.380%   $265.199   $265.20   $265.20   $265.20  
  Purchase #2 $166.26   6.456%   $176.9937   $176.99   $177.00   $177.00  
  Purchase #3 $134.56   4.741%   $140.9395   $140.94   $140.95   $140.90  
  Purchase #4 $233.98   12.448%   $263.1058   $263.11   $263.10   $263.10  
  Purchase #5 $167.80   3.460%   $173.6059   $173.61   $173.60   $173.60  
  Purchase #6 $65.80   10.583%   $72.7636   $72.76   $72.75   $72.80  
  Purchase #7 $115.94   5.260%   $122.0384   $122.04   $122.05   $122.00  
  7 purchase totals = $1,124.60       $1,214.6459   $1,214.65   $1,214.65   $1,214.60