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	$249.98	12.351%	$280.855	$280.86	$280.85	$280.90
Purchase #2	$34.43	9.632%	$37.7463	$37.75	$37.75	$37.70
Purchase #3	$137.83	7.766%	$148.5339	$148.53	$148.55	$148.50
Purchase #4	$29.53	9.355%	$32.2925	$32.29	$32.30	$32.30
Purchase #5	$20.43	8.525%	$22.1717	$22.17	$22.15	$22.20
Purchase #6	$190.59	4.236%	$198.6634	$198.66	$198.65	$198.70
Purchase #7	$50.33	5.583%	$53.1399	$53.14	$53.15	$53.10
7 purchase totals =	$713.12		$773.4027	$773.40	$773.40	$773.40