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 $211.88   3.123%   $218.497   $218.50   $218.50   $218.50  
  Purchase #2 $111.40   11.618%   $124.3425   $124.34   $124.35   $124.30  
  Purchase #3 $112.92   6.201%   $119.9222   $119.92   $119.90   $119.90  
  Purchase #4 $18.34   11.426%   $20.4355   $20.44   $20.45   $20.40  
  Purchase #5 $17.70   10.801%   $19.6118   $19.61   $19.60   $19.60  
  Purchase #6 $36.26   9.326%   $39.6416   $39.64   $39.65   $39.60  
  Purchase #7 $187.68   11.259%   $208.8109   $208.81   $208.80   $208.80  
  7 purchase totals = $696.18       $751.2615   $751.26   $751.25   $751.10