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 $120.98   4.173%   $126.0285   $126.03   $126.05   $126.00  
  Purchase #2 $51.73   10.198%   $57.0054   $57.01   $57.00   $57.00  
  Purchase #3 $52.95   9.431%   $57.9437   $57.94   $57.95   $57.90  
  Purchase #4 $71.34   3.289%   $73.6864   $73.69   $73.70   $73.70  
  Purchase #5 $38.99   11.157%   $43.3401   $43.34   $43.35   $43.30  
  Purchase #6 $73.95   8.456%   $80.2032   $80.20   $80.20   $80.20  
  Purchase #7 $26.93   9.237%   $29.4175   $29.42   $29.40   $29.40  
  7 purchase totals = $436.87       $467.6248   $467.63   $467.65   $467.50