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 $162.55   13.321%   $184.2033   $184.20   $184.20   $184.20  
  Purchase #2 $123.44   9.527%   $135.2001   $135.20   $135.20   $135.20  
  Purchase #3 $99.80   5.786%   $105.5744   $105.57   $105.55   $105.60  
  Purchase #4 $61.87   4.129%   $64.4246   $64.42   $64.40   $64.40  
  Purchase #5 $191.93   7.791%   $206.8833   $206.88   $206.90   $206.90  
  Purchase #6 $138.34   9.699%   $151.7576   $151.76   $151.75   $151.80  
  Purchase #7 $207.73   7.673%   $223.6691   $223.67   $223.65   $223.70  
  7 purchase totals = $985.66       $1,071.7124   $1,071.70   $1,071.65   $1,071.80