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 $233.28   13.178%   $264.0216   $264.02   $264.00   $264.00  
  Purchase #2 $89.99   9.841%   $98.8459   $98.85   $98.85   $98.80  
  Purchase #3 $174.67   13.394%   $198.0653   $198.07   $198.05   $198.10  
  Purchase #4 $158.68   6.230%   $168.5658   $168.57   $168.55   $168.60  
  Purchase #5 $244.71   7.318%   $262.6179   $262.62   $262.60   $262.60  
  Purchase #6 $6.75   6.593%   $7.195   $7.20   $7.20   $7.20  
  Purchase #7 $23.98   12.434%   $26.9617   $26.96   $26.95   $27.00  
  7 purchase totals = $932.06       $1,026.2732   $1,026.29   $1,026.20   $1,026.30