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	$53.74	3.248%	$55.4855	$55.49	$55.50	$55.50
Purchase #2	$87.56	13.216%	$99.1319	$99.13	$99.15	$99.10
Purchase #3	$62.71	13.391%	$71.1075	$71.11	$71.10	$71.10
Purchase #4	$58.37	12.135%	$65.4532	$65.45	$65.45	$65.50
Purchase #5	$50.32	8.704%	$54.6999	$54.70	$54.70	$54.70
Purchase #6	$143.62	8.720%	$156.1437	$156.14	$156.15	$156.10
Purchase #7	$87.89	5.398%	$92.6343	$92.63	$92.65	$92.60
7 purchase totals =	$544.21		$594.6560	$594.65	$594.70	$594.60