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	$88.33	6.741%	$94.2843	$94.28	$94.30	$94.30
Purchase #2	$89.31	6.166%	$94.8169	$94.82	$94.80	$94.80
Purchase #3	$154.49	13.114%	$174.7498	$174.75	$174.75	$174.70
Purchase #4	$144.62	9.185%	$157.9033	$157.90	$157.90	$157.90
Purchase #5	$62.49	9.460%	$68.4016	$68.40	$68.40	$68.40
Purchase #6	$172.77	10.435%	$190.7985	$190.80	$190.80	$190.80
Purchase #7	$227.87	13.613%	$258.8899	$258.89	$258.90	$258.90
7 purchase totals =	$939.88		$1,039.8443	$1,039.84	$1,039.85	$1,039.80