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 $48.51   11.161%   $53.9242   $53.92   $53.90   $53.90  
  Purchase #2 $208.89   13.365%   $236.8081   $236.81   $236.80   $236.80  
  Purchase #3 $185.56   3.705%   $192.435   $192.44   $192.45   $192.40  
  Purchase #4 $153.96   10.445%   $170.0411   $170.04   $170.05   $170.00  
  Purchase #5 $46.77   5.642%   $49.4088   $49.41   $49.40   $49.40  
  Purchase #6 $225.72   3.512%   $233.6473   $233.65   $233.65   $233.60  
  Purchase #7 $26.46   11.495%   $29.5016   $29.50   $29.50   $29.50  
  7 purchase totals = $895.87       $965.7661   $965.77   $965.75   $965.60