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	$242.52	8.573%	$263.3112	$263.31	$263.30	$263.30
Purchase #2	$231.98	6.670%	$247.4531	$247.45	$247.45	$247.50
Purchase #3	$182.65	3.481%	$189.008	$189.01	$189.00	$189.00
Purchase #4	$38.32	9.167%	$41.8328	$41.83	$41.85	$41.80
Purchase #5	$238.66	12.599%	$268.7288	$268.73	$268.75	$268.70
Purchase #6	$18.69	8.471%	$20.2732	$20.27	$20.25	$20.30
Purchase #7	$57.98	4.265%	$60.4528	$60.45	$60.45	$60.50
7 purchase totals =	$1,010.80		$1,091.0599	$1,091.05	$1,091.05	$1,091.10