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 $98.55   10.849%   $109.2417   $109.24   $109.25   $109.20  
  Purchase #2 $24.74   9.480%   $27.0854   $27.09   $27.10   $27.10  
  Purchase #3 $79.77   13.160%   $90.2677   $90.27   $90.25   $90.30  
  Purchase #4 $74.61   13.594%   $84.7525   $84.75   $84.75   $84.80  
  Purchase #5 $104.46   5.865%   $110.5866   $110.59   $110.60   $110.60  
  Purchase #6 $196.92   9.588%   $215.8007   $215.80   $215.80   $215.80  
  Purchase #7 $104.38   13.201%   $118.1592   $118.16   $118.15   $118.20  
  7 purchase totals = $683.43       $755.8938   $755.90   $755.90   $756.00