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	$178.54	5.238%	$187.8919	$187.89	$187.90	$187.90
Purchase #2	$89.99	10.619%	$99.546	$99.55	$99.55	$99.50
Purchase #3	$219.94	4.258%	$229.305	$229.31	$229.30	$229.30
Purchase #4	$192.87	11.620%	$215.2815	$215.28	$215.30	$215.30
Purchase #5	$44.53	13.325%	$50.4636	$50.46	$50.45	$50.50
Purchase #6	$184.71	10.608%	$204.304	$204.30	$204.30	$204.30
Purchase #7	$43.30	13.544%	$49.1646	$49.16	$49.15	$49.20
7 purchase totals =	$953.88		$1,035.9566	$1,035.95	$1,035.95	$1,036.00