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 $187.27   13.202%   $211.9934   $211.99   $212.00   $212.00  
  Purchase #2 $66.75   4.749%   $69.92   $69.92   $69.90   $69.90  
  Purchase #3 $90.25   6.504%   $96.1199   $96.12   $96.10   $96.10  
  Purchase #4 $62.78   12.813%   $70.824   $70.82   $70.80   $70.80  
  Purchase #5 $85.87   13.143%   $97.1559   $97.16   $97.15   $97.20  
  Purchase #6 $193.54   3.138%   $199.6133   $199.61   $199.60   $199.60  
  Purchase #7 $152.46   12.616%   $171.6944   $171.69   $171.70   $171.70  
  7 purchase totals = $838.92       $917.3209   $917.31   $917.25   $917.30