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	$243.31	12.739%	$274.3053	$274.31	$274.30	$274.30
Purchase #2	$83.56	3.633%	$86.5957	$86.60	$86.60	$86.60
Purchase #3	$155.47	6.696%	$165.8803	$165.88	$165.90	$165.90
Purchase #4	$101.69	9.176%	$111.0211	$111.02	$111.00	$111.00
Purchase #5	$155.97	13.396%	$176.8637	$176.86	$176.85	$176.90
Purchase #6	$105.65	12.722%	$119.0908	$119.09	$119.10	$119.10
Purchase #7	$63.43	8.751%	$68.9808	$68.98	$69.00	$69.00
7 purchase totals =	$909.08		$1,002.7377	$1,002.74	$1,002.75	$1,002.80