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 $198.60   13.177%   $224.7695   $224.77   $224.75   $224.80  
  Purchase #2 $67.36   3.867%   $69.9648   $69.96   $69.95   $70.00  
  Purchase #3 $62.30   4.285%   $64.9696   $64.97   $64.95   $65.00  
  Purchase #4 $202.89   10.827%   $224.8569   $224.86   $224.85   $224.90  
  Purchase #5 $242.95   7.860%   $262.0459   $262.05   $262.05   $262.00  
  Purchase #6 $38.48   10.687%   $42.5924   $42.59   $42.60   $42.60  
  Purchase #7 $125.90   9.178%   $137.4551   $137.46   $137.45   $137.50  
  7 purchase totals = $938.48       $1,026.6542   $1,026.66   $1,026.60   $1,026.80