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 $67.37   13.206%   $76.2669   $76.27   $76.25   $76.30  
  Purchase #2 $100.85   3.281%   $104.1589   $104.16   $104.15   $104.20  
  Purchase #3 $98.85   5.235%   $104.0248   $104.02   $104.00   $104.00  
  Purchase #4 $127.64   4.219%   $133.0251   $133.03   $133.05   $133.00  
  Purchase #5 $131.38   9.454%   $143.8007   $143.80   $143.80   $143.80  
  Purchase #6 $164.92   8.459%   $178.8706   $178.87   $178.85   $178.90  
  Purchase #7 $56.65   6.487%   $60.3249   $60.32   $60.30   $60.30  
  7 purchase totals = $747.66       $800.4719   $800.47   $800.40   $800.50