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	$11.91	3.119%	$12.2815	$12.28	$12.30	$12.30
Purchase #2	$114.66	7.264%	$122.9889	$122.99	$123.00	$123.00
Purchase #3	$54.42	3.479%	$56.3133	$56.31	$56.30	$56.30
Purchase #4	$82.91	6.280%	$88.1167	$88.12	$88.10	$88.10
Purchase #5	$32.44	7.288%	$34.8042	$34.80	$34.80	$34.80
Purchase #6	$100.28	3.667%	$103.9573	$103.96	$103.95	$104.00
Purchase #7	$80.83	10.537%	$89.3471	$89.35	$89.35	$89.30
7 purchase totals =	$477.45		$507.8090	$507.81	$507.80	$507.80