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 $68.90   9.783%   $75.6405   $75.64   $75.65   $75.60  
  Purchase #2 $120.69   4.657%   $126.3105   $126.31   $126.30   $126.30  
  Purchase #3 $113.99   4.520%   $119.1423   $119.14   $119.15   $119.10  
  Purchase #4 $109.31   13.321%   $123.8712   $123.87   $123.85   $123.90  
  Purchase #5 $121.29   9.827%   $133.2092   $133.21   $133.20   $133.20  
  Purchase #6 $125.27   13.138%   $141.728   $141.73   $141.75   $141.70  
  Purchase #7 $221.70   4.482%   $231.6366   $231.64   $231.65   $231.60  
  7 purchase totals = $881.15       $951.5383   $951.54   $951.55   $951.40