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 $168.46   8.588%   $182.9273   $182.93   $182.95   $182.90  
  Purchase #2 $224.85   12.489%   $252.9315   $252.93   $252.95   $252.90  
  Purchase #3 $10.91   12.695%   $12.295   $12.30   $12.30   $12.30  
  Purchase #4 $86.61   10.368%   $95.5897   $95.59   $95.60   $95.60  
  Purchase #5 $151.96   3.609%   $157.4442   $157.44   $157.45   $157.40  
  Purchase #6 $112.34   12.550%   $126.4387   $126.44   $126.45   $126.40  
  Purchase #7 $242.54   10.222%   $267.3324   $267.33   $267.35   $267.30  
  7 purchase totals = $997.67       $1,094.9588   $1,094.96   $1,095.05   $1,094.80