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 $90.27   6.631%   $96.2558   $96.26   $96.25   $96.30  
  Purchase #2 $183.75   4.716%   $192.4157   $192.42   $192.40   $192.40  
  Purchase #3 $236.97   10.636%   $262.1741   $262.17   $262.15   $262.20  
  Purchase #4 $234.89   11.584%   $262.0997   $262.10   $262.10   $262.10  
  Purchase #5 $209.99   4.857%   $220.1892   $220.19   $220.20   $220.20  
  Purchase #6 $59.34   9.864%   $65.1933   $65.19   $65.20   $65.20  
  Purchase #7 $239.54   4.719%   $250.8439   $250.84   $250.85   $250.80  
  7 purchase totals = $1,254.75       $1,349.1717   $1,349.17   $1,349.15   $1,349.20