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	$102.71	13.332%	$116.4033	$116.40	$116.40	$116.40
Purchase #2	$131.83	4.152%	$137.3036	$137.30	$137.30	$137.30
Purchase #3	$219.53	6.485%	$233.7665	$233.77	$233.75	$233.80
Purchase #4	$71.62	10.192%	$78.9195	$78.92	$78.90	$78.90
Purchase #5	$50.45	11.310%	$56.1559	$56.16	$56.15	$56.20
Purchase #6	$85.36	3.761%	$88.5704	$88.57	$88.55	$88.60
Purchase #7	$41.89	6.860%	$44.7637	$44.76	$44.75	$44.80
7 purchase totals =	$703.39		$755.8829	$755.88	$755.80	$756.00