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 $194.93   5.732%   $206.1034   $206.10   $206.10   $206.10  
  Purchase #2 $166.43   13.654%   $189.1544   $189.15   $189.15   $189.20  
  Purchase #3 $206.51   7.392%   $221.7752   $221.78   $221.80   $221.80  
  Purchase #4 $148.61   8.531%   $161.2879   $161.29   $161.30   $161.30  
  Purchase #5 $54.67   5.524%   $57.69   $57.69   $57.70   $57.70  
  Purchase #6 $82.35   3.774%   $85.4579   $85.46   $85.45   $85.50  
  Purchase #7 $14.50   8.670%   $15.7572   $15.76   $15.75   $15.80  
  7 purchase totals = $868.00       $937.2260   $937.23   $937.25   $937.40