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	$174.88	5.194%	$183.9633	$183.96	$183.95	$184.00
Purchase #2	$65.70	3.700%	$68.1309	$68.13	$68.15	$68.10
Purchase #3	$88.38	13.735%	$100.519	$100.52	$100.50	$100.50
Purchase #4	$96.39	4.413%	$100.6437	$100.64	$100.65	$100.60
Purchase #5	$68.49	3.728%	$71.0433	$71.04	$71.05	$71.00
Purchase #6	$45.25	12.739%	$51.0144	$51.01	$51.00	$51.00
Purchase #7	$244.69	8.389%	$265.217	$265.22	$265.20	$265.20
7 purchase totals =	$783.78		$840.5316	$840.52	$840.50	$840.40