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	$230.56	11.383%	$256.8046	$256.80	$256.80	$256.80
Purchase #2	$98.41	4.770%	$103.1042	$103.10	$103.10	$103.10
Purchase #3	$102.89	12.773%	$116.0321	$116.03	$116.05	$116.00
Purchase #4	$69.28	9.589%	$75.9233	$75.92	$75.90	$75.90
Purchase #5	$229.91	12.179%	$257.9107	$257.91	$257.90	$257.90
Purchase #6	$134.74	11.549%	$150.3011	$150.30	$150.30	$150.30
Purchase #7	$40.38	13.386%	$45.7853	$45.79	$45.80	$45.80
7 purchase totals =	$906.17		$1,005.8613	$1,005.85	$1,005.85	$1,005.80