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	$96.51	9.378%	$105.5607	$105.56	$105.55	$105.60
Purchase #2	$194.43	3.216%	$200.6829	$200.68	$200.70	$200.70
Purchase #3	$170.77	5.453%	$180.0821	$180.08	$180.10	$180.10
Purchase #4	$21.27	7.730%	$22.9142	$22.91	$22.90	$22.90
Purchase #5	$58.51	10.792%	$64.8244	$64.82	$64.80	$64.80
Purchase #6	$37.71	12.839%	$42.5516	$42.55	$42.55	$42.60
Purchase #7	$17.98	13.653%	$20.4348	$20.43	$20.45	$20.40
7 purchase totals =	$597.18		$637.0507	$637.03	$637.05	$637.10