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 $211.38   13.435%   $239.7789   $239.78   $239.80   $239.80  
  Purchase #2 $28.34   7.359%   $30.4255   $30.43   $30.45   $30.40  
  Purchase #3 $32.50   8.615%   $35.2999   $35.30   $35.30   $35.30  
  Purchase #4 $223.96   5.798%   $236.9452   $236.95   $236.95   $236.90  
  Purchase #5 $231.56   4.128%   $241.1188   $241.12   $241.10   $241.10  
  Purchase #6 $142.27   7.575%   $153.047   $153.05   $153.05   $153.00  
  Purchase #7 $233.93   5.290%   $246.3049   $246.30   $246.30   $246.30  
  7 purchase totals = $1,103.94       $1,182.9202   $1,182.93   $1,182.95   $1,182.80