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	$26.48	10.715%	$29.3173	$29.32	$29.30	$29.30
Purchase #2	$80.26	7.240%	$86.0708	$86.07	$86.05	$86.10
Purchase #3	$166.68	11.498%	$185.8449	$185.84	$185.85	$185.80
Purchase #4	$128.51	13.207%	$145.4823	$145.48	$145.50	$145.50
Purchase #5	$116.75	12.502%	$131.3461	$131.35	$131.35	$131.30
Purchase #6	$199.38	4.401%	$208.1547	$208.15	$208.15	$208.20
Purchase #7	$191.75	10.724%	$212.3133	$212.31	$212.30	$212.30
7 purchase totals =	$909.81		$998.5294	$998.52	$998.50	$998.50