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	$104.97	11.363%	$116.8977	$116.90	$116.90	$116.90
Purchase #2	$80.78	10.829%	$89.5277	$89.53	$89.55	$89.50
Purchase #3	$152.38	9.120%	$166.2771	$166.28	$166.30	$166.30
Purchase #4	$47.64	5.401%	$50.213	$50.21	$50.20	$50.20
Purchase #5	$81.33	13.283%	$92.1331	$92.13	$92.15	$92.10
Purchase #6	$13.47	11.413%	$15.0073	$15.01	$15.00	$15.00
Purchase #7	$203.83	4.699%	$213.408	$213.41	$213.40	$213.40
7 purchase totals =	$684.40		$743.4639	$743.47	$743.50	$743.40