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	$138.58	11.386%	$154.3587	$154.36	$154.35	$154.40
Purchase #2	$169.85	7.612%	$182.779	$182.78	$182.80	$182.80
Purchase #3	$19.41	6.500%	$20.6717	$20.67	$20.65	$20.70
Purchase #4	$98.53	13.326%	$111.6601	$111.66	$111.65	$111.70
Purchase #5	$150.96	5.581%	$159.3851	$159.39	$159.40	$159.40
Purchase #6	$223.45	4.522%	$233.5544	$233.55	$233.55	$233.60
Purchase #7	$99.92	4.233%	$104.1496	$104.15	$104.15	$104.10
7 purchase totals =	$900.70		$966.5586	$966.56	$966.55	$966.70