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	$56.68	5.578%	$59.8416	$59.84	$59.85	$59.80
Purchase #2	$121.33	6.270%	$128.9374	$128.94	$128.95	$128.90
Purchase #3	$233.82	9.415%	$255.8342	$255.83	$255.85	$255.80
Purchase #4	$227.86	3.618%	$236.104	$236.10	$236.10	$236.10
Purchase #5	$21.28	8.772%	$23.1467	$23.15	$23.15	$23.10
Purchase #6	$242.93	8.792%	$264.2884	$264.29	$264.30	$264.30
Purchase #7	$49.26	4.425%	$51.4398	$51.44	$51.45	$51.40
7 purchase totals =	$953.16		$1,019.5921	$1,019.59	$1,019.65	$1,019.40