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	$15.81	3.599%	$16.379	$16.38	$16.40	$16.40
Purchase #2	$153.65	8.480%	$166.6795	$166.68	$166.70	$166.70
Purchase #3	$17.26	4.319%	$18.0055	$18.01	$18.00	$18.00
Purchase #4	$158.96	7.767%	$171.3064	$171.31	$171.30	$171.30
Purchase #5	$90.99	9.491%	$99.6259	$99.63	$99.65	$99.60
Purchase #6	$157.40	9.846%	$172.8976	$172.90	$172.90	$172.90
Purchase #7	$126.44	4.315%	$131.8959	$131.90	$131.90	$131.90
7 purchase totals =	$720.51		$776.7898	$776.81	$776.85	$776.80