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 $152.43   10.190%   $167.9626   $167.96   $167.95   $168.00  
  Purchase #2 $230.35   8.253%   $249.3608   $249.36   $249.35   $249.40  
  Purchase #3 $233.59   7.359%   $250.7799   $250.78   $250.80   $250.80  
  Purchase #4 $247.60   9.669%   $271.5404   $271.54   $271.55   $271.50  
  Purchase #5 $212.83   5.326%   $224.1653   $224.17   $224.15   $224.20  
  Purchase #6 $117.90   8.186%   $127.5513   $127.55   $127.55   $127.60  
  Purchase #7 $186.84   4.378%   $195.0199   $195.02   $195.00   $195.00  
  7 purchase totals = $1,381.54       $1,486.3802   $1,486.38   $1,486.35   $1,486.50