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 $53.99   13.721%   $61.398   $61.40   $61.40   $61.40  
  Purchase #2 $226.48   11.506%   $252.5388   $252.54   $252.55   $252.50  
  Purchase #3 $94.86   4.583%   $99.2074   $99.21   $99.20   $99.20  
  Purchase #4 $66.86   10.506%   $73.8843   $73.88   $73.90   $73.90  
  Purchase #5 $172.37   8.799%   $187.5368   $187.54   $187.55   $187.50  
  Purchase #6 $32.67   12.194%   $36.6538   $36.65   $36.65   $36.70  
  Purchase #7 $236.55   5.460%   $249.4656   $249.47   $249.45   $249.50  
  7 purchase totals = $883.78       $960.6847   $960.69   $960.70   $960.70