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	$37.87	13.846%	$43.1135	$43.11	$43.10	$43.10
Purchase #2	$89.47	13.196%	$101.2765	$101.28	$101.30	$101.30
Purchase #3	$57.82	8.729%	$62.8671	$62.87	$62.85	$62.90
Purchase #4	$36.47	11.493%	$40.6615	$40.66	$40.65	$40.70
Purchase #5	$53.57	5.764%	$56.6578	$56.66	$56.65	$56.70
Purchase #6	$203.66	7.645%	$219.2298	$219.23	$219.25	$219.20
Purchase #7	$60.76	3.190%	$62.6982	$62.70	$62.70	$62.70
7 purchase totals =	$539.62		$586.5044	$586.51	$586.50	$586.60