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	$12.37	5.805%	$13.0881	$13.09	$13.10	$13.10
Purchase #2	$105.85	9.229%	$115.6189	$115.62	$115.60	$115.60
Purchase #3	$21.52	10.841%	$23.853	$23.85	$23.85	$23.90
Purchase #4	$72.82	7.646%	$78.3878	$78.39	$78.40	$78.40
Purchase #5	$37.76	9.539%	$41.3619	$41.36	$41.35	$41.40
Purchase #6	$80.26	11.808%	$89.7371	$89.74	$89.75	$89.70
Purchase #7	$149.80	11.424%	$166.9132	$166.91	$166.90	$166.90
7 purchase totals =	$480.38		$528.9600	$528.96	$528.95	$529.00