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	$108.73	13.774%	$123.7065	$123.71	$123.70	$123.70
Purchase #2	$218.64	11.636%	$244.081	$244.08	$244.10	$244.10
Purchase #3	$111.63	3.391%	$115.4154	$115.42	$115.40	$115.40
Purchase #4	$91.73	9.448%	$100.3967	$100.40	$100.40	$100.40
Purchase #5	$230.63	10.628%	$255.1414	$255.14	$255.15	$255.10
Purchase #6	$14.29	11.325%	$15.9083	$15.91	$15.90	$15.90
Purchase #7	$64.68	4.221%	$67.4101	$67.41	$67.40	$67.40
7 purchase totals =	$840.33		$922.0594	$922.07	$922.05	$922.00