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 $106.64   11.804%   $119.2278   $119.23   $119.25   $119.20  
  Purchase #2 $195.41   6.604%   $208.3149   $208.31   $208.30   $208.30  
  Purchase #3 $59.61   6.694%   $63.6003   $63.60   $63.60   $63.60  
  Purchase #4 $158.25   7.420%   $169.9922   $169.99   $170.00   $170.00  
  Purchase #5 $26.69   10.373%   $29.4586   $29.46   $29.45   $29.50  
  Purchase #6 $234.32   3.190%   $241.7948   $241.79   $241.80   $241.80  
  Purchase #7 $75.67   7.205%   $81.122   $81.12   $81.10   $81.10  
  7 purchase totals = $856.59       $913.5106   $913.50   $913.50   $913.50