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	$210.68	7.176%	$225.7984	$225.80	$225.80	$225.80
Purchase #2	$116.30	6.526%	$123.8897	$123.89	$123.90	$123.90
Purchase #3	$227.61	9.870%	$250.0751	$250.08	$250.10	$250.10
Purchase #4	$121.42	9.786%	$133.3022	$133.30	$133.30	$133.30
Purchase #5	$35.66	11.604%	$39.798	$39.80	$39.80	$39.80
Purchase #6	$79.51	12.529%	$89.4718	$89.47	$89.45	$89.50
Purchase #7	$73.77	9.857%	$81.0415	$81.04	$81.05	$81.00
7 purchase totals =	$864.95		$943.3767	$943.38	$943.40	$943.40