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 $102.27   5.858%   $108.261   $108.26   $108.25   $108.30  
  Purchase #2 $154.77   7.486%   $166.3561   $166.36   $166.35   $166.40  
  Purchase #3 $191.88   8.617%   $208.4143   $208.41   $208.40   $208.40  
  Purchase #4 $81.50   11.821%   $91.1341   $91.13   $91.15   $91.10  
  Purchase #5 $175.63   11.173%   $195.2531   $195.25   $195.25   $195.30  
  Purchase #6 $232.44   4.558%   $243.0346   $243.03   $243.05   $243.00  
  Purchase #7 $57.69   4.212%   $60.1199   $60.12   $60.10   $60.10  
  7 purchase totals = $996.18       $1,072.5731   $1,072.56   $1,072.55   $1,072.60