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	$159.33	12.205%	$178.7762	$178.78	$178.80	$178.80
Purchase #2	$62.57	3.210%	$64.5785	$64.58	$64.60	$64.60
Purchase #3	$41.93	4.597%	$43.8575	$43.86	$43.85	$43.90
Purchase #4	$17.72	13.257%	$20.0691	$20.07	$20.05	$20.10
Purchase #5	$85.51	4.146%	$89.0552	$89.06	$89.05	$89.10
Purchase #6	$67.95	11.825%	$75.9851	$75.99	$76.00	$76.00
Purchase #7	$106.39	4.700%	$111.3903	$111.39	$111.40	$111.40
7 purchase totals =	$541.40		$583.7119	$583.73	$583.75	$583.90