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	$95.46	5.142%	$100.3686	$100.37	$100.35	$100.40
Purchase #2	$91.63	13.191%	$103.7169	$103.72	$103.70	$103.70
Purchase #3	$181.93	3.671%	$188.6087	$188.61	$188.60	$188.60
Purchase #4	$28.27	10.173%	$31.1459	$31.15	$31.15	$31.10
Purchase #5	$152.70	4.248%	$159.1867	$159.19	$159.20	$159.20
Purchase #6	$124.55	5.823%	$131.8025	$131.80	$131.80	$131.80
Purchase #7	$77.67	7.329%	$83.3624	$83.36	$83.35	$83.40
7 purchase totals =	$752.21		$798.1917	$798.20	$798.15	$798.20