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	$6.72	8.408%	$7.285	$7.29	$7.30	$7.30
Purchase #2	$33.82	12.564%	$38.0691	$38.07	$38.05	$38.10
Purchase #3	$166.82	13.427%	$189.2189	$189.22	$189.20	$189.20
Purchase #4	$111.81	5.672%	$118.1519	$118.15	$118.15	$118.20
Purchase #5	$12.60	13.740%	$14.3312	$14.33	$14.35	$14.30
Purchase #6	$144.57	9.356%	$158.096	$158.10	$158.10	$158.10
Purchase #7	$125.72	4.319%	$131.1498	$131.15	$131.15	$131.10
7 purchase totals =	$602.06		$656.3019	$656.31	$656.30	$656.30