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	$199.97	13.307%	$226.58	$226.58	$226.60	$226.60
Purchase #2	$78.75	13.575%	$89.4403	$89.44	$89.45	$89.40
Purchase #3	$234.56	3.846%	$243.5812	$243.58	$243.60	$243.60
Purchase #4	$74.77	7.431%	$80.3262	$80.33	$80.35	$80.30
Purchase #5	$242.62	10.662%	$268.4881	$268.49	$268.50	$268.50
Purchase #6	$47.32	8.530%	$51.3564	$51.36	$51.35	$51.40
Purchase #7	$124.62	13.251%	$141.1334	$141.13	$141.15	$141.10
7 purchase totals =	$1,002.61		$1,100.9056	$1,100.91	$1,101.00	$1,100.90