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	$36.79	9.486%	$40.2799	$40.28	$40.30	$40.30
Purchase #2	$86.44	7.499%	$92.9221	$92.92	$92.90	$92.90
Purchase #3	$147.90	3.689%	$153.356	$153.36	$153.35	$153.40
Purchase #4	$35.35	5.789%	$37.3964	$37.40	$37.40	$37.40
Purchase #5	$138.34	5.301%	$145.6734	$145.67	$145.65	$145.70
Purchase #6	$96.64	8.433%	$104.7897	$104.79	$104.80	$104.80
Purchase #7	$180.83	4.300%	$188.6057	$188.61	$188.60	$188.60
7 purchase totals =	$722.29		$763.0232	$763.03	$763.00	$763.10