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 $60.56   5.561%   $63.9277   $63.93   $63.95   $63.90  
  Purchase #2 $247.43   13.822%   $281.6298   $281.63   $281.65   $281.60  
  Purchase #3 $209.79   12.528%   $236.0725   $236.07   $236.05   $236.10  
  Purchase #4 $177.56   12.867%   $200.4066   $200.41   $200.40   $200.40  
  Purchase #5 $187.86   10.181%   $206.986   $206.99   $207.00   $207.00  
  Purchase #6 $29.66   4.175%   $30.8983   $30.90   $30.90   $30.90  
  Purchase #7 $239.99   3.112%   $247.4585   $247.46   $247.45   $247.50  
  7 purchase totals = $1,152.85       $1,267.3794   $1,267.39   $1,267.40   $1,267.40