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	$77.87	6.174%	$82.6777	$82.68	$82.70	$82.70
Purchase #2	$181.56	13.699%	$206.4319	$206.43	$206.45	$206.40
Purchase #3	$57.89	4.839%	$60.6913	$60.69	$60.70	$60.70
Purchase #4	$232.62	11.837%	$260.1552	$260.16	$260.15	$260.20
Purchase #5	$168.79	3.860%	$175.3053	$175.31	$175.30	$175.30
Purchase #6	$98.93	12.379%	$111.1765	$111.18	$111.20	$111.20
Purchase #7	$46.98	12.827%	$53.0061	$53.01	$53.00	$53.00
7 purchase totals =	$864.64		$949.4440	$949.46	$949.50	$949.50