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	$231.60	4.768%	$242.6427	$242.64	$242.65	$242.60
Purchase #2	$123.78	3.242%	$127.7929	$127.79	$127.80	$127.80
Purchase #3	$99.37	13.125%	$112.4123	$112.41	$112.40	$112.40
Purchase #4	$80.88	7.174%	$86.6823	$86.68	$86.70	$86.70
Purchase #5	$223.84	4.365%	$233.6106	$233.61	$233.60	$233.60
Purchase #6	$150.77	5.735%	$159.4167	$159.42	$159.40	$159.40
Purchase #7	$72.52	6.133%	$76.9677	$76.97	$76.95	$77.00
7 purchase totals =	$982.76		$1,039.5252	$1,039.52	$1,039.50	$1,039.50