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	$169.30	9.284%	$185.0178	$185.02	$185.00	$185.00
Purchase #2	$35.50	10.328%	$39.1664	$39.17	$39.15	$39.20
Purchase #3	$173.83	8.698%	$188.9497	$188.95	$188.95	$188.90
Purchase #4	$143.42	10.542%	$158.5393	$158.54	$158.55	$158.50
Purchase #5	$38.39	4.746%	$40.212	$40.21	$40.20	$40.20
Purchase #6	$185.85	3.173%	$191.747	$191.75	$191.75	$191.70
Purchase #7	$35.66	3.270%	$36.8261	$36.83	$36.85	$36.80
7 purchase totals =	$781.95		$840.4583	$840.47	$840.45	$840.30