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	$15.40	7.384%	$16.5371	$16.54	$16.55	$16.50
Purchase #2	$89.72	8.446%	$97.2978	$97.30	$97.30	$97.30
Purchase #3	$127.75	11.246%	$142.1168	$142.12	$142.10	$142.10
Purchase #4	$161.39	10.542%	$178.4037	$178.40	$178.40	$178.40
Purchase #5	$57.87	5.651%	$61.1402	$61.14	$61.15	$61.10
Purchase #6	$242.29	4.476%	$253.1349	$253.13	$253.15	$253.10
Purchase #7	$41.92	4.791%	$43.9284	$43.93	$43.95	$43.90
7 purchase totals =	$736.34		$792.5589	$792.56	$792.60	$792.40