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	$216.99	11.610%	$242.1825	$242.18	$242.20	$242.20
Purchase #2	$151.81	4.791%	$159.0832	$159.08	$159.10	$159.10
Purchase #3	$73.91	6.274%	$78.5471	$78.55	$78.55	$78.50
Purchase #4	$37.45	10.306%	$41.3096	$41.31	$41.30	$41.30
Purchase #5	$38.47	12.516%	$43.2849	$43.28	$43.30	$43.30
Purchase #6	$69.65	12.197%	$78.1452	$78.15	$78.15	$78.10
Purchase #7	$96.89	9.613%	$106.204	$106.20	$106.20	$106.20
7 purchase totals =	$685.17		$748.7565	$748.75	$748.80	$748.70