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	$236.75	12.765%	$266.9711	$266.97	$266.95	$267.00
Purchase #2	$156.73	10.323%	$172.9092	$172.91	$172.90	$172.90
Purchase #3	$25.54	12.143%	$28.6413	$28.64	$28.65	$28.60
Purchase #4	$30.34	11.495%	$33.8276	$33.83	$33.85	$33.80
Purchase #5	$241.62	9.203%	$263.8563	$263.86	$263.85	$263.90
Purchase #6	$139.87	4.250%	$145.8145	$145.81	$145.80	$145.80
Purchase #7	$126.92	3.774%	$131.71	$131.71	$131.70	$131.70
7 purchase totals =	$957.77		$1,043.7300	$1,043.73	$1,043.70	$1,043.70