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 $89.35   5.197%   $93.9935   $93.99   $94.00   $94.00  
  Purchase #2 $21.75   13.524%   $24.6915   $24.69   $24.70   $24.70  
  Purchase #3 $236.77   5.584%   $249.9912   $249.99   $250.00   $250.00  
  Purchase #4 $32.46   12.868%   $36.637   $36.64   $36.65   $36.60  
  Purchase #5 $70.31   7.646%   $75.6859   $75.69   $75.70   $75.70  
  Purchase #6 $161.79   3.556%   $167.5433   $167.54   $167.55   $167.50  
  Purchase #7 $196.98   8.629%   $213.9774   $213.98   $214.00   $214.00  
  7 purchase totals = $809.41       $862.5198   $862.52   $862.60   $862.50