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	$155.33	10.137%	$171.0758	$171.08	$171.10	$171.10
Purchase #2	$222.55	11.156%	$247.3777	$247.38	$247.40	$247.40
Purchase #3	$177.66	3.616%	$184.0842	$184.08	$184.10	$184.10
Purchase #4	$83.56	7.797%	$90.0752	$90.08	$90.10	$90.10
Purchase #5	$194.49	12.826%	$219.4353	$219.44	$219.45	$219.40
Purchase #6	$225.63	3.274%	$233.0171	$233.02	$233.00	$233.00
Purchase #7	$132.56	10.490%	$146.4655	$146.47	$146.45	$146.50
7 purchase totals =	$1,191.78		$1,291.5308	$1,291.55	$1,291.60	$1,291.60