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	$247.54	13.216%	$280.2549	$280.25	$280.25	$280.30
Purchase #2	$50.84	6.526%	$54.1578	$54.16	$54.15	$54.20
Purchase #3	$76.89	3.388%	$79.495	$79.50	$79.50	$79.50
Purchase #4	$214.48	12.510%	$241.3114	$241.31	$241.30	$241.30
Purchase #5	$28.50	7.169%	$30.5432	$30.54	$30.55	$30.50
Purchase #6	$89.54	10.679%	$99.102	$99.10	$99.10	$99.10
Purchase #7	$6.89	9.214%	$7.5248	$7.52	$7.50	$7.50
7 purchase totals =	$714.68		$792.3891	$792.38	$792.35	$792.40