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	$19.60	6.510%	$20.876	$20.88	$20.90	$20.90
Purchase #2	$232.85	8.634%	$252.9543	$252.95	$252.95	$253.00
Purchase #3	$96.91	6.711%	$103.4136	$103.41	$103.40	$103.40
Purchase #4	$46.31	13.244%	$52.4433	$52.44	$52.45	$52.40
Purchase #5	$181.28	7.764%	$195.3546	$195.35	$195.35	$195.40
Purchase #6	$224.36	13.690%	$255.0749	$255.07	$255.05	$255.10
Purchase #7	$168.30	7.523%	$180.9612	$180.96	$180.95	$181.00
7 purchase totals =	$969.61		$1,061.0779	$1,061.06	$1,061.05	$1,061.20