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	$210.78	3.367%	$217.877	$217.88	$217.90	$217.90
Purchase #2	$196.92	12.447%	$221.4306	$221.43	$221.45	$221.40
Purchase #3	$43.64	8.287%	$47.2564	$47.26	$47.25	$47.30
Purchase #4	$71.91	11.288%	$80.0272	$80.03	$80.05	$80.00
Purchase #5	$93.50	13.204%	$105.8457	$105.85	$105.85	$105.80
Purchase #6	$44.81	3.699%	$46.4675	$46.47	$46.45	$46.50
Purchase #7	$92.57	13.561%	$105.1234	$105.12	$105.10	$105.10
7 purchase totals =	$754.13		$824.0278	$824.04	$824.05	$824.00