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 $233.68   8.822%   $254.2952   $254.30   $254.30   $254.30  
  Purchase #2 $128.82   11.261%   $143.3264   $143.33   $143.35   $143.30  
  Purchase #3 $230.92   10.241%   $254.5685   $254.57   $254.55   $254.60  
  Purchase #4 $201.55   3.214%   $208.0278   $208.03   $208.05   $208.00  
  Purchase #5 $243.94   3.548%   $252.595   $252.60   $252.60   $252.60  
  Purchase #6 $69.93   4.364%   $72.9817   $72.98   $73.00   $73.00  
  Purchase #7 $187.81   5.381%   $197.9161   $197.92   $197.90   $197.90  
  7 purchase totals = $1,296.65       $1,383.7107   $1,383.73   $1,383.75   $1,383.70