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 $217.42   7.489%   $233.7026   $233.70   $233.70   $233.70  
  Purchase #2 $69.76   13.312%   $79.0465   $79.05   $79.05   $79.00  
  Purchase #3 $61.67   10.704%   $68.2712   $68.27   $68.25   $68.30  
  Purchase #4 $136.85   8.614%   $148.6383   $148.64   $148.65   $148.60  
  Purchase #5 $144.57   3.395%   $149.4782   $149.48   $149.50   $149.50  
  Purchase #6 $146.36   13.766%   $166.5079   $166.51   $166.50   $166.50  
  Purchase #7 $188.50   13.659%   $214.2472   $214.25   $214.25   $214.20  
  7 purchase totals = $965.13       $1,059.8919   $1,059.90   $1,059.90   $1,059.80