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 $46.61   12.509%   $52.4404   $52.44   $52.45   $52.40  
  Purchase #2 $67.28   9.181%   $73.457   $73.46   $73.45   $73.50  
  Purchase #3 $161.83   6.132%   $171.7534   $171.75   $171.75   $171.80  
  Purchase #4 $142.64   8.118%   $154.2195   $154.22   $154.20   $154.20  
  Purchase #5 $52.94   6.634%   $56.452   $56.45   $56.45   $56.50  
  Purchase #6 $199.96   7.440%   $214.837   $214.84   $214.85   $214.80  
  Purchase #7 $89.69   13.329%   $101.6448   $101.64   $101.65   $101.60  
  7 purchase totals = $760.95       $824.8041   $824.80   $824.80   $824.80