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	$78.54	12.833%	$88.619	$88.62	$88.60	$88.60
Purchase #2	$48.28	9.851%	$53.0361	$53.04	$53.05	$53.00
Purchase #3	$193.38	3.239%	$199.6436	$199.64	$199.65	$199.60
Purchase #4	$50.73	8.820%	$55.2044	$55.20	$55.20	$55.20
Purchase #5	$119.40	3.711%	$123.8309	$123.83	$123.85	$123.80
Purchase #6	$6.61	12.868%	$7.4606	$7.46	$7.45	$7.50
Purchase #7	$232.89	8.482%	$252.6437	$252.64	$252.65	$252.60
7 purchase totals =	$729.83		$780.4383	$780.43	$780.45	$780.30