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 $58.67   13.329%   $66.4901   $66.49   $66.50   $66.50  
  Purchase #2 $197.69   8.713%   $214.9147   $214.91   $214.90   $214.90  
  Purchase #3 $145.68   11.248%   $162.0661   $162.07   $162.05   $162.10  
  Purchase #4 $140.67   4.284%   $146.6963   $146.70   $146.70   $146.70  
  Purchase #5 $195.48   4.563%   $204.3998   $204.40   $204.40   $204.40  
  Purchase #6 $169.75   13.543%   $192.7392   $192.74   $192.75   $192.70  
  Purchase #7 $111.67   11.285%   $124.272   $124.27   $124.25   $124.30  
  7 purchase totals = $1,019.61       $1,111.5782   $1,111.58   $1,111.55   $1,111.60