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	$59.68	12.828%	$67.3358	$67.34	$67.35	$67.30
Purchase #2	$172.64	4.206%	$179.9012	$179.90	$179.90	$179.90
Purchase #3	$158.27	13.829%	$180.1572	$180.16	$180.15	$180.20
Purchase #4	$54.30	8.439%	$58.8824	$58.88	$58.90	$58.90
Purchase #5	$128.71	6.681%	$137.3091	$137.31	$137.30	$137.30
Purchase #6	$87.45	10.608%	$96.7267	$96.73	$96.75	$96.70
Purchase #7	$10.83	5.240%	$11.3975	$11.40	$11.40	$11.40
7 purchase totals =	$671.88		$731.7099	$731.72	$731.75	$731.70