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 $94.43   4.167%   $98.3649   $98.36   $98.35   $98.40  
  Purchase #2 $93.42   11.522%   $104.1839   $104.18   $104.20   $104.20  
  Purchase #3 $43.41   3.783%   $45.0522   $45.05   $45.05   $45.10  
  Purchase #4 $49.51   6.502%   $52.7291   $52.73   $52.75   $52.70  
  Purchase #5 $164.79   7.728%   $177.525   $177.53   $177.55   $177.50  
  Purchase #6 $174.87   12.206%   $196.2146   $196.21   $196.20   $196.20  
  Purchase #7 $112.69   10.219%   $124.2058   $124.21   $124.20   $124.20  
  7 purchase totals = $733.12       $798.2755   $798.27   $798.30   $798.30