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 $92.42   6.615%   $98.5336   $98.53   $98.55   $98.50  
  Purchase #2 $198.38   4.649%   $207.6027   $207.60   $207.60   $207.60  
  Purchase #3 $68.68   3.505%   $71.0872   $71.09   $71.10   $71.10  
  Purchase #4 $98.39   10.611%   $108.8302   $108.83   $108.85   $108.80  
  Purchase #5 $101.60   8.194%   $109.9251   $109.93   $109.95   $109.90  
  Purchase #6 $241.63   13.502%   $274.2549   $274.25   $274.25   $274.30  
  Purchase #7 $138.69   6.454%   $147.6411   $147.64   $147.65   $147.60  
  7 purchase totals = $939.79       $1,017.8748   $1,017.87   $1,017.95   $1,017.80