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 $62.60   5.412%   $65.9879   $65.99   $66.00   $66.00  
  Purchase #2 $22.45   6.267%   $23.8569   $23.86   $23.85   $23.90  
  Purchase #3 $176.66   11.801%   $197.5076   $197.51   $197.50   $197.50  
  Purchase #4 $80.87   10.608%   $89.4487   $89.45   $89.45   $89.40  
  Purchase #5 $179.62   4.531%   $187.7586   $187.76   $187.75   $187.80  
  Purchase #6 $43.93   6.750%   $46.8953   $46.90   $46.90   $46.90  
  Purchase #7 $112.72   3.369%   $116.5175   $116.52   $116.50   $116.50  
  7 purchase totals = $678.85       $727.9725   $727.99   $727.95   $728.00