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 $83.99   13.378%   $95.2262   $95.23   $95.25   $95.20  
  Purchase #2 $192.61   7.697%   $207.4352   $207.44   $207.45   $207.40  
  Purchase #3 $47.48   11.608%   $52.9915   $52.99   $53.00   $53.00  
  Purchase #4 $68.30   6.829%   $72.9642   $72.96   $72.95   $73.00  
  Purchase #5 $21.28   12.555%   $23.9517   $23.95   $23.95   $24.00  
  Purchase #6 $104.35   8.795%   $113.5276   $113.53   $113.55   $113.50  
  Purchase #7 $66.37   13.518%   $75.3419   $75.34   $75.35   $75.30  
  7 purchase totals = $584.38       $641.4383   $641.44   $641.50   $641.40