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	$76.59	8.792%	$83.3238	$83.32	$83.30	$83.30
Purchase #2	$150.35	13.479%	$170.6157	$170.62	$170.60	$170.60
Purchase #3	$93.43	6.710%	$99.6992	$99.70	$99.70	$99.70
Purchase #4	$35.56	6.142%	$37.7441	$37.74	$37.75	$37.70
Purchase #5	$88.50	9.453%	$96.8659	$96.87	$96.85	$96.90
Purchase #6	$74.41	5.326%	$78.3731	$78.37	$78.35	$78.40
Purchase #7	$189.31	8.256%	$204.9394	$204.94	$204.95	$204.90
7 purchase totals =	$708.15		$771.5612	$771.56	$771.50	$771.50