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	$13.90	10.235%	$15.3227	$15.32	$15.30	$15.30
Purchase #2	$96.92	9.107%	$105.7465	$105.75	$105.75	$105.70
Purchase #3	$151.50	5.482%	$159.8052	$159.81	$159.80	$159.80
Purchase #4	$39.30	5.436%	$41.4363	$41.44	$41.45	$41.40
Purchase #5	$35.89	6.398%	$38.1862	$38.19	$38.20	$38.20
Purchase #6	$88.67	12.859%	$100.0721	$100.07	$100.05	$100.10
Purchase #7	$28.89	12.671%	$32.5507	$32.55	$32.55	$32.60
7 purchase totals =	$455.07		$493.1197	$493.13	$493.10	$493.10