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 $236.84   13.844%   $269.6281   $269.63   $269.65   $269.60  
  Purchase #2 $43.48   7.627%   $46.7962   $46.80   $46.80   $46.80  
  Purchase #3 $242.89   4.550%   $253.9415   $253.94   $253.95   $253.90  
  Purchase #4 $249.76   11.707%   $278.9994   $279.00   $279.00   $279.00  
  Purchase #5 $130.61   13.337%   $148.0295   $148.03   $148.05   $148.00  
  Purchase #6 $243.39   12.167%   $273.0033   $273.00   $273.00   $273.00  
  Purchase #7 $217.52   6.406%   $231.4543   $231.45   $231.45   $231.50  
  7 purchase totals = $1,364.49       $1,501.8523   $1,501.85   $1,501.90   $1,501.80