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 $98.93   4.719%   $103.5985   $103.60   $103.60   $103.60  
  Purchase #2 $249.31   5.570%   $263.1966   $263.20   $263.20   $263.20  
  Purchase #3 $13.76   5.626%   $14.5341   $14.53   $14.55   $14.50  
  Purchase #4 $52.30   7.225%   $56.0787   $56.08   $56.10   $56.10  
  Purchase #5 $208.33   6.518%   $221.9089   $221.91   $221.90   $221.90  
  Purchase #6 $128.78   11.820%   $144.0018   $144.00   $144.00   $144.00  
  Purchase #7 $46.30   11.542%   $51.6439   $51.64   $51.65   $51.60  
  7 purchase totals = $797.71       $854.9625   $854.96   $855.00   $854.90