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	$30.60	11.842%	$34.2237	$34.22	$34.20	$34.20
Purchase #2	$43.48	4.576%	$45.4696	$45.47	$45.45	$45.50
Purchase #3	$75.87	10.154%	$83.5738	$83.57	$83.55	$83.60
Purchase #4	$180.41	6.229%	$191.6477	$191.65	$191.65	$191.60
Purchase #5	$125.57	11.293%	$139.7506	$139.75	$139.75	$139.80
Purchase #6	$146.50	4.703%	$153.3899	$153.39	$153.40	$153.40
Purchase #7	$229.69	11.666%	$256.4856	$256.49	$256.50	$256.50
7 purchase totals =	$832.12		$904.5409	$904.54	$904.50	$904.60