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	$180.43	4.160%	$187.9359	$187.94	$187.95	$187.90
Purchase #2	$71.56	12.220%	$80.3046	$80.30	$80.30	$80.30
Purchase #3	$48.27	10.561%	$53.3678	$53.37	$53.35	$53.40
Purchase #4	$190.53	7.506%	$204.8312	$204.83	$204.85	$204.80
Purchase #5	$178.31	12.209%	$200.0799	$200.08	$200.10	$200.10
Purchase #6	$49.28	12.834%	$55.6046	$55.60	$55.60	$55.60
Purchase #7	$111.74	5.730%	$118.1427	$118.14	$118.15	$118.10
7 purchase totals =	$830.12		$900.2667	$900.26	$900.30	$900.20