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	$37.98	6.560%	$40.4715	$40.47	$40.45	$40.50
Purchase #2	$230.44	11.504%	$256.9498	$256.95	$256.95	$256.90
Purchase #3	$191.73	13.339%	$217.3049	$217.30	$217.30	$217.30
Purchase #4	$81.33	13.422%	$92.2461	$92.25	$92.25	$92.20
Purchase #5	$218.44	5.577%	$230.6224	$230.62	$230.60	$230.60
Purchase #6	$41.33	3.138%	$42.6269	$42.63	$42.65	$42.60
Purchase #7	$204.92	3.373%	$211.832	$211.83	$211.85	$211.80
7 purchase totals =	$1,006.17		$1,092.0536	$1,092.05	$1,092.05	$1,091.90