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 $235.25   8.248%   $254.6534   $254.65   $254.65   $254.70  
  Purchase #2 $233.51   13.802%   $265.7391   $265.74   $265.75   $265.70  
  Purchase #3 $168.27   9.846%   $184.8379   $184.84   $184.85   $184.80  
  Purchase #4 $16.40   9.288%   $17.9232   $17.92   $17.90   $17.90  
  Purchase #5 $164.47   7.525%   $176.8464   $176.85   $176.85   $176.80  
  Purchase #6 $105.84   4.146%   $110.2281   $110.23   $110.25   $110.20  
  Purchase #7 $20.94   10.522%   $23.1433   $23.14   $23.15   $23.10  
  7 purchase totals = $944.68       $1,033.3714   $1,033.37   $1,033.40   $1,033.20