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	$140.56	8.715%	$152.8098	$152.81	$152.80	$152.80
Purchase #2	$79.45	3.794%	$82.4643	$82.46	$82.45	$82.50
Purchase #3	$217.80	13.440%	$247.0723	$247.07	$247.05	$247.10
Purchase #4	$58.58	4.363%	$61.1358	$61.14	$61.15	$61.10
Purchase #5	$60.31	6.343%	$64.1355	$64.14	$64.15	$64.10
Purchase #6	$181.44	5.609%	$191.617	$191.62	$191.60	$191.60
Purchase #7	$101.39	8.173%	$109.6766	$109.68	$109.70	$109.70
7 purchase totals =	$839.53		$908.9113	$908.92	$908.90	$908.90