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	$39.52	9.211%	$43.1602	$43.16	$43.15	$43.20
Purchase #2	$40.56	6.394%	$43.1534	$43.15	$43.15	$43.20
Purchase #3	$209.55	13.406%	$237.6423	$237.64	$237.65	$237.60
Purchase #4	$229.59	10.850%	$254.5005	$254.50	$254.50	$254.50
Purchase #5	$38.36	6.619%	$40.899	$40.90	$40.90	$40.90
Purchase #6	$161.60	6.316%	$171.8067	$171.81	$171.80	$171.80
Purchase #7	$25.67	6.469%	$27.3306	$27.33	$27.35	$27.30
7 purchase totals =	$744.85		$818.4927	$818.49	$818.50	$818.50