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 $178.94   9.540%   $196.0109   $196.01   $196.00   $196.00  
  Purchase #2 $114.62   10.183%   $126.2918   $126.29   $126.30   $126.30  
  Purchase #3 $197.43   4.392%   $206.1011   $206.10   $206.10   $206.10  
  Purchase #4 $90.93   8.682%   $98.8245   $98.82   $98.80   $98.80  
  Purchase #5 $177.94   7.347%   $191.0133   $191.01   $191.00   $191.00  
  Purchase #6 $179.33   5.156%   $188.5763   $188.58   $188.60   $188.60  
  Purchase #7 $43.29   10.852%   $47.9878   $47.99   $48.00   $48.00  
  7 purchase totals = $982.48       $1,054.8057   $1,054.80   $1,054.80   $1,054.80