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 $96.89   11.458%   $107.9917   $107.99   $108.00   $108.00  
  Purchase #2 $152.29   12.251%   $170.947   $170.95   $170.95   $170.90  
  Purchase #3 $156.88   4.824%   $164.4479   $164.45   $164.45   $164.40  
  Purchase #4 $197.34   8.831%   $214.7671   $214.77   $214.75   $214.80  
  Purchase #5 $158.75   10.823%   $175.9315   $175.93   $175.95   $175.90  
  Purchase #6 $223.67   5.697%   $236.4125   $236.41   $236.40   $236.40  
  Purchase #7 $178.60   11.559%   $199.2444   $199.24   $199.25   $199.20  
  7 purchase totals = $1,164.42       $1,269.7421   $1,269.74   $1,269.75   $1,269.60