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	$136.89	11.418%	$152.5201	$152.52	$152.50	$152.50
Purchase #2	$200.64	4.720%	$210.1102	$210.11	$210.10	$210.10
Purchase #3	$186.43	13.445%	$211.4955	$211.50	$211.50	$211.50
Purchase #4	$174.80	11.139%	$194.271	$194.27	$194.25	$194.30
Purchase #5	$108.58	9.497%	$118.8918	$118.89	$118.90	$118.90
Purchase #6	$6.73	13.203%	$7.6186	$7.62	$7.60	$7.60
Purchase #7	$172.91	3.364%	$178.7267	$178.73	$178.75	$178.70
7 purchase totals =	$986.98		$1,073.6339	$1,073.64	$1,073.60	$1,073.60