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	$30.91	4.453%	$32.2864	$32.29	$32.30	$32.30
Purchase #2	$93.40	5.743%	$98.764	$98.76	$98.75	$98.80
Purchase #3	$117.93	10.619%	$130.453	$130.45	$130.45	$130.50
Purchase #4	$72.81	7.301%	$78.1259	$78.13	$78.15	$78.10
Purchase #5	$77.59	11.598%	$86.5889	$86.59	$86.60	$86.60
Purchase #6	$96.38	9.749%	$105.7761	$105.78	$105.80	$105.80
Purchase #7	$25.68	10.806%	$28.455	$28.46	$28.45	$28.50
7 purchase totals =	$514.70		$560.4493	$560.46	$560.50	$560.60