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	$183.98	12.831%	$207.5865	$207.59	$207.60	$207.60
Purchase #2	$148.79	7.404%	$159.8064	$159.81	$159.80	$159.80
Purchase #3	$35.49	13.631%	$40.3276	$40.33	$40.35	$40.30
Purchase #4	$34.91	10.498%	$38.5749	$38.57	$38.55	$38.60
Purchase #5	$218.82	11.610%	$244.225	$244.23	$244.25	$244.20
Purchase #6	$111.93	10.570%	$123.761	$123.76	$123.75	$123.80
Purchase #7	$110.79	7.492%	$119.0904	$119.09	$119.10	$119.10
7 purchase totals =	$844.71		$933.3718	$933.38	$933.40	$933.40