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	$111.63	7.750%	$120.2813	$120.28	$120.30	$120.30
Purchase #2	$91.78	8.192%	$99.2986	$99.30	$99.30	$99.30
Purchase #3	$217.35	10.393%	$239.9392	$239.94	$239.95	$239.90
Purchase #4	$223.82	7.275%	$240.1029	$240.10	$240.10	$240.10
Purchase #5	$137.49	9.239%	$150.1927	$150.19	$150.20	$150.20
Purchase #6	$78.53	4.795%	$82.2955	$82.30	$82.30	$82.30
Purchase #7	$73.51	13.128%	$83.1604	$83.16	$83.15	$83.20
7 purchase totals =	$934.11		$1,015.2706	$1,015.27	$1,015.30	$1,015.30