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	$31.75	6.670%	$33.8677	$33.87	$33.85	$33.90
Purchase #2	$118.29	12.781%	$133.4086	$133.41	$133.40	$133.40
Purchase #3	$128.73	3.307%	$132.9871	$132.99	$133.00	$133.00
Purchase #4	$77.53	10.305%	$85.5195	$85.52	$85.50	$85.50
Purchase #5	$41.56	11.218%	$46.2222	$46.22	$46.20	$46.20
Purchase #6	$94.74	4.786%	$99.2743	$99.27	$99.25	$99.30
Purchase #7	$27.77	13.811%	$31.6053	$31.61	$31.60	$31.60
7 purchase totals =	$520.37		$562.8847	$562.89	$562.80	$562.90