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	$132.35	8.155%	$143.1431	$143.14	$143.15	$143.10
Purchase #2	$81.92	8.783%	$89.115	$89.12	$89.10	$89.10
Purchase #3	$42.53	3.222%	$43.9003	$43.90	$43.90	$43.90
Purchase #4	$248.79	7.595%	$267.6856	$267.69	$267.70	$267.70
Purchase #5	$44.37	3.450%	$45.9008	$45.90	$45.90	$45.90
Purchase #6	$95.47	8.609%	$103.689	$103.69	$103.70	$103.70
Purchase #7	$139.63	6.152%	$148.22	$148.22	$148.20	$148.20
7 purchase totals =	$785.06		$841.6538	$841.66	$841.65	$841.60