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	$248.40	13.163%	$281.0969	$281.10	$281.10	$281.10
Purchase #2	$111.41	12.481%	$125.3151	$125.32	$125.30	$125.30
Purchase #3	$101.77	9.233%	$111.1664	$111.17	$111.15	$111.20
Purchase #4	$119.31	7.258%	$127.9695	$127.97	$127.95	$128.00
Purchase #5	$232.30	11.493%	$258.9982	$259.00	$259.00	$259.00
Purchase #6	$44.55	9.802%	$48.9168	$48.92	$48.90	$48.90
Purchase #7	$243.80	11.518%	$271.8809	$271.88	$271.90	$271.90
7 purchase totals =	$1,101.54		$1,225.3438	$1,225.36	$1,225.30	$1,225.40