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	$211.85	10.130%	$233.3104	$233.31	$233.30	$233.30
Purchase #2	$111.91	11.235%	$124.4831	$124.48	$124.50	$124.50
Purchase #3	$55.39	10.690%	$61.3112	$61.31	$61.30	$61.30
Purchase #4	$102.61	8.375%	$111.2036	$111.20	$111.20	$111.20
Purchase #5	$46.77	12.477%	$52.6055	$52.61	$52.60	$52.60
Purchase #6	$79.88	3.459%	$82.643	$82.64	$82.65	$82.60
Purchase #7	$34.64	10.542%	$38.2917	$38.29	$38.30	$38.30
7 purchase totals =	$643.05		$703.8485	$703.84	$703.85	$703.80