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 $198.30   10.404%   $218.9311   $218.93   $218.95   $218.90  
  Purchase #2 $220.61   11.470%   $245.914   $245.91   $245.90   $245.90  
  Purchase #3 $228.62   9.252%   $249.7719   $249.77   $249.75   $249.80  
  Purchase #4 $125.74   11.521%   $140.2265   $140.23   $140.25   $140.20  
  Purchase #5 $172.32   13.512%   $195.6039   $195.60   $195.60   $195.60  
  Purchase #6 $120.67   12.704%   $135.9999   $136.00   $136.00   $136.00  
  Purchase #7 $47.49   8.841%   $51.6886   $51.69   $51.70   $51.70  
  7 purchase totals = $1,113.75       $1,238.1359   $1,238.13   $1,238.15   $1,238.10