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	$26.91	7.671%	$28.9743	$28.97	$28.95	$29.00
Purchase #2	$9.49	11.613%	$10.5921	$10.59	$10.60	$10.60
Purchase #3	$186.96	3.564%	$193.6233	$193.62	$193.60	$193.60
Purchase #4	$121.60	8.437%	$131.8594	$131.86	$131.85	$131.90
Purchase #5	$144.47	4.393%	$150.8166	$150.82	$150.80	$150.80
Purchase #6	$248.48	8.134%	$268.6914	$268.69	$268.70	$268.70
Purchase #7	$89.92	11.591%	$100.3426	$100.34	$100.35	$100.30
7 purchase totals =	$827.83		$884.8997	$884.89	$884.85	$884.90