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	$78.40	3.527%	$81.1652	$81.17	$81.15	$81.20
Purchase #2	$54.84	6.108%	$58.1896	$58.19	$58.20	$58.20
Purchase #3	$79.57	3.838%	$82.6239	$82.62	$82.60	$82.60
Purchase #4	$96.64	7.241%	$103.6377	$103.64	$103.65	$103.60
Purchase #5	$73.72	4.826%	$77.2777	$77.28	$77.30	$77.30
Purchase #6	$97.85	4.111%	$101.8726	$101.87	$101.85	$101.90
Purchase #7	$73.93	11.467%	$82.4076	$82.41	$82.40	$82.40
7 purchase totals =	$554.95		$587.1743	$587.18	$587.15	$587.20