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 $96.76   8.522%   $105.0059   $105.01   $105.00   $105.00  
  Purchase #2 $104.75   10.327%   $115.5675   $115.57   $115.55   $115.60  
  Purchase #3 $209.59   6.413%   $223.031   $223.03   $223.05   $223.00  
  Purchase #4 $65.46   11.211%   $72.7987   $72.80   $72.80   $72.80  
  Purchase #5 $62.86   5.677%   $66.4286   $66.43   $66.45   $66.40  
  Purchase #6 $44.35   5.213%   $46.662   $46.66   $46.65   $46.70  
  Purchase #7 $217.85   13.858%   $248.0397   $248.04   $248.05   $248.00  
  7 purchase totals = $801.62       $877.5334   $877.54   $877.55   $877.50