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 $44.98   11.139%   $49.9903   $49.99   $50.00   $50.00  
  Purchase #2 $65.85   10.502%   $72.7656   $72.77   $72.75   $72.80  
  Purchase #3 $228.99   11.191%   $254.6163   $254.62   $254.60   $254.60  
  Purchase #4 $240.79   7.688%   $259.3019   $259.30   $259.30   $259.30  
  Purchase #5 $179.95   4.218%   $187.5403   $187.54   $187.55   $187.50  
  Purchase #6 $21.85   6.727%   $23.3198   $23.32   $23.30   $23.30  
  Purchase #7 $83.54   3.322%   $86.3152   $86.32   $86.30   $86.30  
  7 purchase totals = $865.95       $933.8494   $933.86   $933.80   $933.80