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	$171.45	4.644%	$179.4121	$179.41	$179.40	$179.40
Purchase #2	$250.30	3.264%	$258.4698	$258.47	$258.45	$258.50
Purchase #3	$97.51	9.345%	$106.6223	$106.62	$106.60	$106.60
Purchase #4	$220.66	7.557%	$237.3353	$237.34	$237.35	$237.30
Purchase #5	$188.53	10.809%	$208.9082	$208.91	$208.90	$208.90
Purchase #6	$248.46	13.428%	$281.8232	$281.82	$281.80	$281.80
Purchase #7	$40.36	4.663%	$42.242	$42.24	$42.25	$42.20
7 purchase totals =	$1,217.27		$1,314.8129	$1,314.81	$1,314.75	$1,314.70