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 $89.79   6.688%   $95.7952   $95.80   $95.80   $95.80  
  Purchase #2 $186.98   10.537%   $206.6821   $206.68   $206.70   $206.70  
  Purchase #3 $47.60   8.451%   $51.6227   $51.62   $51.60   $51.60  
  Purchase #4 $133.63   12.619%   $150.4928   $150.49   $150.50   $150.50  
  Purchase #5 $229.96   9.729%   $252.3328   $252.33   $252.35   $252.30  
  Purchase #6 $35.62   8.469%   $38.6367   $38.64   $38.65   $38.60  
  Purchase #7 $117.80   5.412%   $124.1753   $124.18   $124.20   $124.20  
  7 purchase totals = $841.38       $919.7376   $919.74   $919.80   $919.70