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	$150.91	9.643%	$165.4623	$165.46	$165.45	$165.50
Purchase #2	$107.41	6.115%	$113.9781	$113.98	$114.00	$114.00
Purchase #3	$172.42	13.843%	$196.2881	$196.29	$196.30	$196.30
Purchase #4	$198.49	12.714%	$223.726	$223.73	$223.75	$223.70
Purchase #5	$72.84	10.309%	$80.3491	$80.35	$80.35	$80.30
Purchase #6	$36.82	9.638%	$40.3687	$40.37	$40.35	$40.40
Purchase #7	$105.53	5.501%	$111.3352	$111.34	$111.35	$111.30
7 purchase totals =	$844.42		$931.5075	$931.52	$931.55	$931.50