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	$134.48	10.752%	$148.9393	$148.94	$148.95	$148.90
Purchase #2	$89.28	11.793%	$99.8088	$99.81	$99.80	$99.80
Purchase #3	$82.54	7.488%	$88.7206	$88.72	$88.70	$88.70
Purchase #4	$223.91	13.477%	$254.0864	$254.09	$254.10	$254.10
Purchase #5	$230.94	10.640%	$255.512	$255.51	$255.50	$255.50
Purchase #6	$10.30	4.540%	$10.7676	$10.77	$10.75	$10.80
Purchase #7	$47.36	10.801%	$52.4754	$52.48	$52.50	$52.50
7 purchase totals =	$818.81		$910.3101	$910.32	$910.30	$910.30