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	$223.75	3.191%	$230.8899	$230.89	$230.90	$230.90
Purchase #2	$159.57	5.395%	$168.1788	$168.18	$168.20	$168.20
Purchase #3	$209.65	10.554%	$231.7765	$231.78	$231.80	$231.80
Purchase #4	$81.74	12.651%	$92.0809	$92.08	$92.10	$92.10
Purchase #5	$136.30	12.335%	$153.1126	$153.11	$153.10	$153.10
Purchase #6	$169.89	9.167%	$185.4638	$185.46	$185.45	$185.50
Purchase #7	$123.86	12.343%	$139.148	$139.15	$139.15	$139.10
7 purchase totals =	$1,104.76		$1,200.6505	$1,200.65	$1,200.70	$1,200.70