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	$108.30	3.338%	$111.9151	$111.92	$111.90	$111.90
Purchase #2	$76.75	7.132%	$82.2238	$82.22	$82.20	$82.20
Purchase #3	$249.91	10.616%	$276.4404	$276.44	$276.45	$276.40
Purchase #4	$127.45	13.856%	$145.1095	$145.11	$145.10	$145.10
Purchase #5	$224.30	10.631%	$248.1453	$248.15	$248.15	$248.10
Purchase #6	$126.69	10.767%	$140.3307	$140.33	$140.35	$140.30
Purchase #7	$97.78	4.723%	$102.3981	$102.40	$102.40	$102.40
7 purchase totals =	$1,011.18		$1,106.5629	$1,106.57	$1,106.55	$1,106.40