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	$146.91	9.646%	$161.0809	$161.08	$161.10	$161.10
Purchase #2	$52.81	12.172%	$59.238	$59.24	$59.25	$59.20
Purchase #3	$55.82	10.302%	$61.5706	$61.57	$61.55	$61.60
Purchase #4	$49.30	11.654%	$55.0454	$55.05	$55.05	$55.00
Purchase #5	$174.73	9.768%	$191.7976	$191.80	$191.80	$191.80
Purchase #6	$85.28	10.686%	$94.393	$94.39	$94.40	$94.40
Purchase #7	$53.63	6.445%	$57.0865	$57.09	$57.10	$57.10
7 purchase totals =	$618.48		$680.2120	$680.22	$680.25	$680.20