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	$152.46	6.178%	$161.879	$161.88	$161.90	$161.90
Purchase #2	$54.61	4.182%	$56.8938	$56.89	$56.90	$56.90
Purchase #3	$226.87	12.309%	$254.7954	$254.80	$254.80	$254.80
Purchase #4	$82.40	3.849%	$85.5716	$85.57	$85.55	$85.60
Purchase #5	$77.77	11.109%	$86.4095	$86.41	$86.40	$86.40
Purchase #6	$17.85	13.472%	$20.2548	$20.25	$20.25	$20.30
Purchase #7	$243.70	13.209%	$275.8903	$275.89	$275.90	$275.90
7 purchase totals =	$855.66		$941.6944	$941.69	$941.70	$941.80