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	$244.44	6.846%	$261.1744	$261.17	$261.15	$261.20
Purchase #2	$123.36	12.119%	$138.31	$138.31	$138.30	$138.30
Purchase #3	$92.84	8.870%	$101.0749	$101.07	$101.05	$101.10
Purchase #4	$52.34	10.736%	$57.9592	$57.96	$57.95	$58.00
Purchase #5	$52.83	12.834%	$59.6102	$59.61	$59.60	$59.60
Purchase #6	$230.37	11.446%	$256.7382	$256.74	$256.75	$256.70
Purchase #7	$117.70	8.169%	$127.3149	$127.31	$127.30	$127.30
7 purchase totals =	$913.88		$1,002.1818	$1,002.17	$1,002.10	$1,002.20