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	$99.47	7.176%	$106.608	$106.61	$106.60	$106.60
Purchase #2	$57.84	7.452%	$62.1502	$62.15	$62.15	$62.20
Purchase #3	$84.59	4.461%	$88.3636	$88.36	$88.35	$88.40
Purchase #4	$67.31	4.398%	$70.2703	$70.27	$70.25	$70.30
Purchase #5	$18.70	11.836%	$20.9133	$20.91	$20.90	$20.90
Purchase #6	$226.47	4.817%	$237.3791	$237.38	$237.40	$237.40
Purchase #7	$51.81	7.665%	$55.7812	$55.78	$55.80	$55.80
7 purchase totals =	$606.19		$641.4657	$641.46	$641.45	$641.60