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	$101.40	10.374%	$111.9192	$111.92	$111.90	$111.90
Purchase #2	$65.35	10.719%	$72.3549	$72.35	$72.35	$72.40
Purchase #3	$192.84	9.485%	$211.1309	$211.13	$211.15	$211.10
Purchase #4	$115.28	4.805%	$120.8192	$120.82	$120.80	$120.80
Purchase #5	$115.92	10.242%	$127.7925	$127.79	$127.80	$127.80
Purchase #6	$60.96	4.287%	$63.5734	$63.57	$63.55	$63.60
Purchase #7	$106.86	5.496%	$112.733	$112.73	$112.75	$112.70
7 purchase totals =	$758.61		$820.3231	$820.31	$820.30	$820.30