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 $110.47   12.292%   $124.049   $124.05   $124.05   $124.00  
  Purchase #2 $213.49   9.527%   $233.8292   $233.83   $233.85   $233.80  
  Purchase #3 $51.71   4.506%   $54.0401   $54.04   $54.05   $54.00  
  Purchase #4 $149.36   3.564%   $154.6832   $154.68   $154.70   $154.70  
  Purchase #5 $73.42   3.763%   $76.1828   $76.18   $76.20   $76.20  
  Purchase #6 $187.93   11.110%   $208.809   $208.81   $208.80   $208.80  
  Purchase #7 $31.35   12.770%   $35.3534   $35.35   $35.35   $35.40  
  7 purchase totals = $817.73       $886.9467   $886.94   $887.00   $886.90