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 $111.70   13.566%   $126.8532   $126.85   $126.85   $126.90  
  Purchase #2 $18.61   7.762%   $20.0545   $20.05   $20.05   $20.10  
  Purchase #3 $101.35   13.214%   $114.7424   $114.74   $114.75   $114.70  
  Purchase #4 $199.79   5.175%   $210.1291   $210.13   $210.15   $210.10  
  Purchase #5 $209.28   6.331%   $222.5295   $222.53   $222.55   $222.50  
  Purchase #6 $116.33   7.376%   $124.9105   $124.91   $124.90   $124.90  
  Purchase #7 $192.66   10.670%   $213.2168   $213.22   $213.20   $213.20  
  7 purchase totals = $949.72       $1,032.4360   $1,032.43   $1,032.45   $1,032.40