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	$247.91	10.352%	$273.5736	$273.57	$273.55	$273.60
Purchase #2	$215.77	3.184%	$222.6401	$222.64	$222.65	$222.60
Purchase #3	$49.30	8.339%	$53.4111	$53.41	$53.40	$53.40
Purchase #4	$59.69	4.361%	$62.2931	$62.29	$62.30	$62.30
Purchase #5	$81.98	9.456%	$89.732	$89.73	$89.75	$89.70
Purchase #6	$111.51	6.486%	$118.7425	$118.74	$118.75	$118.70
Purchase #7	$217.87	7.677%	$234.5959	$234.60	$234.60	$234.60
7 purchase totals =	$984.03		$1,054.9883	$1,054.98	$1,055.00	$1,054.90