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 $187.69   13.748%   $213.4936   $213.49   $213.50   $213.50  
  Purchase #2 $171.61   3.506%   $177.6266   $177.63   $177.65   $177.60  
  Purchase #3 $46.96   5.368%   $49.4808   $49.48   $49.50   $49.50  
  Purchase #4 $232.42   12.725%   $261.9954   $262.00   $262.00   $262.00  
  Purchase #5 $244.68   7.474%   $262.9674   $262.97   $262.95   $263.00  
  Purchase #6 $40.60   11.261%   $45.172   $45.17   $45.15   $45.20  
  Purchase #7 $46.52   13.758%   $52.9202   $52.92   $52.90   $52.90  
  7 purchase totals = $970.48       $1,063.6560   $1,063.66   $1,063.65   $1,063.70