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	$63.91	11.813%	$71.4597	$71.46	$71.45	$71.50
Purchase #2	$218.83	13.821%	$249.0745	$249.07	$249.05	$249.10
Purchase #3	$52.52	10.212%	$57.8833	$57.88	$57.90	$57.90
Purchase #4	$245.84	12.240%	$275.9308	$275.93	$275.95	$275.90
Purchase #5	$80.52	9.741%	$88.3635	$88.36	$88.35	$88.40
Purchase #6	$179.56	4.472%	$187.5899	$187.59	$187.60	$187.60
Purchase #7	$25.92	10.773%	$28.7124	$28.71	$28.70	$28.70
7 purchase totals =	$867.10		$959.0141	$959.00	$959.00	$959.10