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	$148.31	4.342%	$154.7496	$154.75	$154.75	$154.70
Purchase #2	$65.61	10.842%	$72.7234	$72.72	$72.70	$72.70
Purchase #3	$70.25	12.272%	$78.8711	$78.87	$78.85	$78.90
Purchase #4	$118.25	5.835%	$125.1499	$125.15	$125.15	$125.10
Purchase #5	$162.29	6.621%	$173.0352	$173.04	$173.05	$173.00
Purchase #6	$87.37	13.645%	$99.2916	$99.29	$99.30	$99.30
Purchase #7	$124.37	11.837%	$139.0917	$139.09	$139.10	$139.10
7 purchase totals =	$776.45		$842.9125	$842.91	$842.90	$842.80