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	$67.51	5.428%	$71.1744	$71.17	$71.15	$71.20
Purchase #2	$153.71	9.174%	$167.8114	$167.81	$167.80	$167.80
Purchase #3	$201.65	4.255%	$210.2302	$210.23	$210.25	$210.20
Purchase #4	$97.74	7.704%	$105.2699	$105.27	$105.25	$105.30
Purchase #5	$247.48	8.117%	$267.568	$267.57	$267.55	$267.60
Purchase #6	$226.35	13.479%	$256.8597	$256.86	$256.85	$256.90
Purchase #7	$221.37	3.478%	$229.0692	$229.07	$229.05	$229.10
7 purchase totals =	$1,215.81		$1,307.9828	$1,307.98	$1,307.90	$1,308.10