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	$162.46	5.283%	$171.0428	$171.04	$171.05	$171.00
Purchase #2	$96.66	13.743%	$109.944	$109.94	$109.95	$109.90
Purchase #3	$44.39	9.602%	$48.6523	$48.65	$48.65	$48.70
Purchase #4	$101.98	3.329%	$105.3749	$105.37	$105.35	$105.40
Purchase #5	$158.92	8.468%	$172.3773	$172.38	$172.40	$172.40
Purchase #6	$156.26	6.323%	$166.1403	$166.14	$166.15	$166.10
Purchase #7	$45.86	5.273%	$48.2782	$48.28	$48.30	$48.30
7 purchase totals =	$766.53		$821.8098	$821.80	$821.85	$821.80