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	$188.59	8.389%	$204.4108	$204.41	$204.40	$204.40
Purchase #2	$181.59	13.127%	$205.4273	$205.43	$205.45	$205.40
Purchase #3	$122.89	9.297%	$134.3151	$134.32	$134.30	$134.30
Purchase #4	$97.98	10.422%	$108.1915	$108.19	$108.20	$108.20
Purchase #5	$83.41	7.314%	$89.5106	$89.51	$89.50	$89.50
Purchase #6	$103.30	12.663%	$116.3809	$116.38	$116.40	$116.40
Purchase #7	$207.75	6.414%	$221.0751	$221.08	$221.10	$221.10
7 purchase totals =	$985.51		$1,079.3113	$1,079.32	$1,079.35	$1,079.30