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	$128.99	12.199%	$144.7255	$144.73	$144.75	$144.70
Purchase #2	$79.53	12.428%	$89.414	$89.41	$89.40	$89.40
Purchase #3	$65.47	8.767%	$71.2098	$71.21	$71.20	$71.20
Purchase #4	$87.75	10.613%	$97.0629	$97.06	$97.05	$97.10
Purchase #5	$74.86	5.425%	$78.9212	$78.92	$78.90	$78.90
Purchase #6	$47.78	4.196%	$49.7848	$49.78	$49.80	$49.80
Purchase #7	$110.99	3.492%	$114.8658	$114.87	$114.85	$114.90
7 purchase totals =	$595.37		$645.9840	$645.98	$645.95	$646.00