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	$89.30	12.195%	$100.1901	$100.19	$100.20	$100.20
Purchase #2	$182.37	13.769%	$207.4805	$207.48	$207.50	$207.50
Purchase #3	$53.41	10.842%	$59.2007	$59.20	$59.20	$59.20
Purchase #4	$61.86	7.367%	$66.4172	$66.42	$66.40	$66.40
Purchase #5	$130.80	9.641%	$143.4104	$143.41	$143.40	$143.40
Purchase #6	$148.96	4.135%	$155.1195	$155.12	$155.10	$155.10
Purchase #7	$63.68	10.694%	$70.4899	$70.49	$70.50	$70.50
7 purchase totals =	$730.38		$802.3083	$802.31	$802.30	$802.30