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	$126.94	3.727%	$131.6711	$131.67	$131.65	$131.70
Purchase #2	$46.68	3.296%	$48.2186	$48.22	$48.20	$48.20
Purchase #3	$19.42	12.711%	$21.8885	$21.89	$21.90	$21.90
Purchase #4	$171.59	10.183%	$189.063	$189.06	$189.05	$189.10
Purchase #5	$158.70	8.767%	$172.6132	$172.61	$172.60	$172.60
Purchase #6	$164.46	8.552%	$178.5246	$178.52	$178.50	$178.50
Purchase #7	$92.61	3.814%	$96.1421	$96.14	$96.15	$96.10
7 purchase totals =	$780.40		$838.1211	$838.11	$838.05	$838.10