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	$100.28	8.535%	$108.8389	$108.84	$108.85	$108.80
Purchase #2	$31.41	3.717%	$32.5775	$32.58	$32.60	$32.60
Purchase #3	$208.95	9.331%	$228.4471	$228.45	$228.45	$228.40
Purchase #4	$53.87	10.396%	$59.4703	$59.47	$59.45	$59.50
Purchase #5	$6.49	4.743%	$6.7978	$6.80	$6.80	$6.80
Purchase #6	$6.92	5.780%	$7.32	$7.32	$7.30	$7.30
Purchase #7	$211.59	13.353%	$239.8436	$239.84	$239.85	$239.80
7 purchase totals =	$619.51		$683.2952	$683.30	$683.30	$683.20