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	$41.66	8.400%	$45.1594	$45.16	$45.15	$45.20
Purchase #2	$138.94	10.429%	$153.4301	$153.43	$153.45	$153.40
Purchase #3	$107.89	6.731%	$115.1521	$115.15	$115.15	$115.20
Purchase #4	$53.91	13.558%	$61.2191	$61.22	$61.20	$61.20
Purchase #5	$102.90	8.645%	$111.7957	$111.80	$111.80	$111.80
Purchase #6	$80.36	10.663%	$88.9288	$88.93	$88.95	$88.90
Purchase #7	$174.61	8.599%	$189.6247	$189.62	$189.60	$189.60
7 purchase totals =	$700.27		$765.3099	$765.31	$765.30	$765.30