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	$120.33	6.740%	$128.4402	$128.44	$128.45	$128.40
Purchase #2	$239.70	7.719%	$258.2024	$258.20	$258.20	$258.20
Purchase #3	$48.58	10.142%	$53.507	$53.51	$53.50	$53.50
Purchase #4	$78.91	4.464%	$82.4325	$82.43	$82.45	$82.40
Purchase #5	$117.91	8.239%	$127.6246	$127.62	$127.60	$127.60
Purchase #6	$89.55	5.404%	$94.3893	$94.39	$94.40	$94.40
Purchase #7	$70.88	3.174%	$73.1297	$73.13	$73.15	$73.10
7 purchase totals =	$765.86		$817.7257	$817.72	$817.75	$817.60