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	$145.91	9.396%	$159.6197	$159.62	$159.60	$159.60
Purchase #2	$154.69	10.332%	$170.6726	$170.67	$170.65	$170.70
Purchase #3	$41.51	11.153%	$46.1396	$46.14	$46.15	$46.10
Purchase #4	$204.45	9.637%	$224.1528	$224.15	$224.15	$224.20
Purchase #5	$82.39	3.516%	$85.2868	$85.29	$85.30	$85.30
Purchase #6	$37.32	12.289%	$41.9063	$41.91	$41.90	$41.90
Purchase #7	$156.59	6.712%	$167.1003	$167.10	$167.10	$167.10
7 purchase totals =	$822.86		$894.8781	$894.88	$894.85	$894.90