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	$96.82	9.363%	$105.8853	$105.89	$105.90	$105.90
Purchase #2	$230.51	5.113%	$242.296	$242.30	$242.30	$242.30
Purchase #3	$44.62	8.457%	$48.3935	$48.39	$48.40	$48.40
Purchase #4	$205.89	4.524%	$215.2045	$215.20	$215.20	$215.20
Purchase #5	$81.39	9.870%	$89.4232	$89.42	$89.40	$89.40
Purchase #6	$210.49	11.414%	$234.5153	$234.52	$234.50	$234.50
Purchase #7	$91.73	13.774%	$104.3649	$104.36	$104.35	$104.40
7 purchase totals =	$961.45		$1,040.0827	$1,040.08	$1,040.05	$1,040.10