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	$207.59	10.649%	$229.6963	$229.70	$229.70	$229.70
Purchase #2	$50.66	13.461%	$57.4793	$57.48	$57.50	$57.50
Purchase #3	$199.92	7.250%	$214.4142	$214.41	$214.40	$214.40
Purchase #4	$104.43	7.580%	$112.3458	$112.35	$112.35	$112.30
Purchase #5	$80.52	12.811%	$90.8354	$90.84	$90.85	$90.80
Purchase #6	$19.44	7.268%	$20.8529	$20.85	$20.85	$20.90
Purchase #7	$244.64	13.706%	$278.1704	$278.17	$278.15	$278.20
7 purchase totals =	$907.20		$1,003.7943	$1,003.80	$1,003.80	$1,003.80