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 $51.63   8.505%   $56.0211   $56.02   $56.00   $56.00  
  Purchase #2 $161.44   9.291%   $176.4394   $176.44   $176.45   $176.40  
  Purchase #3 $86.73   9.804%   $95.233   $95.23   $95.25   $95.20  
  Purchase #4 $178.30   3.511%   $184.5601   $184.56   $184.55   $184.60  
  Purchase #5 $209.82   9.495%   $229.7424   $229.74   $229.75   $229.70  
  Purchase #6 $163.33   10.524%   $180.5188   $180.52   $180.50   $180.50  
  Purchase #7 $61.39   6.599%   $65.4411   $65.44   $65.45   $65.40  
  7 purchase totals = $912.64       $987.9559   $987.95   $987.95   $987.80