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	$84.87	5.849%	$89.834	$89.83	$89.85	$89.80
Purchase #2	$224.52	10.156%	$247.3223	$247.32	$247.30	$247.30
Purchase #3	$198.97	13.267%	$225.3673	$225.37	$225.35	$225.40
Purchase #4	$188.45	11.733%	$210.5608	$210.56	$210.55	$210.60
Purchase #5	$90.68	9.170%	$98.9954	$99.00	$99.00	$99.00
Purchase #6	$41.52	10.490%	$45.8754	$45.88	$45.90	$45.90
Purchase #7	$159.92	9.215%	$174.6566	$174.66	$174.65	$174.70
7 purchase totals =	$988.93		$1,092.6118	$1,092.62	$1,092.60	$1,092.70