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	$77.39	6.458%	$82.3878	$82.39	$82.40	$82.40
Purchase #2	$186.56	4.192%	$194.3806	$194.38	$194.40	$194.40
Purchase #3	$39.91	13.113%	$45.1434	$45.14	$45.15	$45.10
Purchase #4	$240.91	10.749%	$266.8054	$266.81	$266.80	$266.80
Purchase #5	$126.32	4.231%	$131.6646	$131.66	$131.65	$131.70
Purchase #6	$149.39	12.307%	$167.7754	$167.78	$167.80	$167.80
Purchase #7	$216.82	7.514%	$233.1119	$233.11	$233.10	$233.10
7 purchase totals =	$1,037.30		$1,121.2691	$1,121.27	$1,121.30	$1,121.30