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	$180.47	13.304%	$204.4797	$204.48	$204.50	$204.50
Purchase #2	$192.72	8.118%	$208.365	$208.37	$208.35	$208.40
Purchase #3	$168.80	7.537%	$181.5225	$181.52	$181.50	$181.50
Purchase #4	$175.28	11.839%	$196.0314	$196.03	$196.05	$196.00
Purchase #5	$244.49	4.414%	$255.2818	$255.28	$255.30	$255.30
Purchase #6	$7.31	12.724%	$8.2401	$8.24	$8.25	$8.20
Purchase #7	$89.36	8.280%	$96.759	$96.76	$96.75	$96.80
7 purchase totals =	$1,058.43		$1,150.6795	$1,150.68	$1,150.70	$1,150.70