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	$30.67	8.630%	$33.3168	$33.32	$33.30	$33.30
Purchase #2	$73.45	10.250%	$80.9786	$80.98	$81.00	$81.00
Purchase #3	$36.97	4.487%	$38.6288	$38.63	$38.65	$38.60
Purchase #4	$62.60	12.640%	$70.5126	$70.51	$70.50	$70.50
Purchase #5	$204.27	8.346%	$221.3184	$221.32	$221.30	$221.30
Purchase #6	$120.62	5.780%	$127.5918	$127.59	$127.60	$127.60
Purchase #7	$194.90	8.657%	$211.7725	$211.77	$211.75	$211.80
7 purchase totals =	$723.48		$784.1195	$784.12	$784.10	$784.10