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	$196.85	12.478%	$221.4129	$221.41	$221.40	$221.40
Purchase #2	$93.27	4.714%	$97.6667	$97.67	$97.65	$97.70
Purchase #3	$57.47	12.328%	$64.5549	$64.55	$64.55	$64.60
Purchase #4	$113.89	6.139%	$120.8817	$120.88	$120.90	$120.90
Purchase #5	$26.68	6.866%	$28.5118	$28.51	$28.50	$28.50
Purchase #6	$36.78	10.197%	$40.5305	$40.53	$40.55	$40.50
Purchase #7	$100.52	4.821%	$105.3661	$105.37	$105.35	$105.40
7 purchase totals =	$625.46		$678.9246	$678.92	$678.90	$679.00