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 $66.85   12.561%   $75.247   $75.25   $75.25   $75.20  
  Purchase #2 $165.87   6.172%   $176.1075   $176.11   $176.10   $176.10  
  Purchase #3 $173.80   13.233%   $196.799   $196.80   $196.80   $196.80  
  Purchase #4 $132.30   10.789%   $146.5738   $146.57   $146.55   $146.60  
  Purchase #5 $42.84   7.406%   $46.0127   $46.01   $46.00   $46.00  
  Purchase #6 $126.63   5.639%   $133.7707   $133.77   $133.75   $133.80  
  Purchase #7 $35.90   6.597%   $38.2683   $38.27   $38.25   $38.30  
  7 purchase totals = $744.19       $812.7790   $812.78   $812.70   $812.80