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	$73.44	12.721%	$82.7823	$82.78	$82.80	$82.80
Purchase #2	$199.75	4.291%	$208.3213	$208.32	$208.30	$208.30
Purchase #3	$145.65	5.557%	$153.7438	$153.74	$153.75	$153.70
Purchase #4	$95.29	6.405%	$101.3933	$101.39	$101.40	$101.40
Purchase #5	$223.80	3.121%	$230.7848	$230.78	$230.80	$230.80
Purchase #6	$57.60	3.496%	$59.6137	$59.61	$59.60	$59.60
Purchase #7	$58.63	9.765%	$64.3552	$64.36	$64.35	$64.40
7 purchase totals =	$854.16		$900.9944	$900.98	$901.00	$901.00