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	$93.68	6.683%	$99.9406	$99.94	$99.95	$99.90
Purchase #2	$116.51	4.252%	$121.464	$121.46	$121.45	$121.50
Purchase #3	$35.47	5.137%	$37.2921	$37.29	$37.30	$37.30
Purchase #4	$45.61	6.558%	$48.6011	$48.60	$48.60	$48.60
Purchase #5	$131.83	6.303%	$140.1392	$140.14	$140.15	$140.10
Purchase #6	$148.88	11.123%	$165.4399	$165.44	$165.45	$165.40
Purchase #7	$13.35	3.324%	$13.7938	$13.79	$13.80	$13.80
7 purchase totals =	$585.33		$626.6707	$626.66	$626.70	$626.60