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	$232.42	11.398%	$258.9112	$258.91	$258.90	$258.90
Purchase #2	$86.72	11.388%	$96.5957	$96.60	$96.60	$96.60
Purchase #3	$188.97	12.507%	$212.6045	$212.60	$212.60	$212.60
Purchase #4	$174.45	10.324%	$192.4602	$192.46	$192.45	$192.50
Purchase #5	$248.81	8.153%	$269.0955	$269.10	$269.10	$269.10
Purchase #6	$82.87	3.340%	$85.6379	$85.64	$85.65	$85.60
Purchase #7	$52.31	9.208%	$57.1267	$57.13	$57.15	$57.10
7 purchase totals =	$1,066.55		$1,172.4317	$1,172.44	$1,172.45	$1,172.40