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 $24.87   8.299%   $26.934   $26.93   $26.95   $26.90  
  Purchase #2 $166.31   11.772%   $185.888   $185.89   $185.90   $185.90  
  Purchase #3 $33.90   3.533%   $35.0977   $35.10   $35.10   $35.10  
  Purchase #4 $231.65   10.774%   $256.608   $256.61   $256.60   $256.60  
  Purchase #5 $176.73   7.167%   $189.3962   $189.40   $189.40   $189.40  
  Purchase #6 $236.94   7.510%   $254.7342   $254.73   $254.75   $254.70  
  Purchase #7 $223.96   4.718%   $234.5264   $234.53   $234.55   $234.50  
  7 purchase totals = $1,094.36       $1,183.1845   $1,183.19   $1,183.25   $1,183.10