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	$93.37	6.291%	$99.2439	$99.24	$99.25	$99.20
Purchase #2	$156.85	4.523%	$163.9443	$163.94	$163.95	$163.90
Purchase #3	$10.94	8.297%	$11.8477	$11.85	$11.85	$11.80
Purchase #4	$118.54	7.678%	$127.6415	$127.64	$127.65	$127.60
Purchase #5	$80.69	12.450%	$90.7359	$90.74	$90.75	$90.70
Purchase #6	$57.27	7.675%	$61.6655	$61.67	$61.65	$61.70
Purchase #7	$218.41	5.250%	$229.8765	$229.88	$229.90	$229.90
7 purchase totals =	$736.07		$784.9553	$784.96	$785.00	$784.80