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	$17.70	4.180%	$18.4399	$18.44	$18.45	$18.40
Purchase #2	$100.77	8.237%	$109.0704	$109.07	$109.05	$109.10
Purchase #3	$82.87	10.152%	$91.283	$91.28	$91.30	$91.30
Purchase #4	$245.98	7.721%	$264.9721	$264.97	$264.95	$265.00
Purchase #5	$18.50	9.734%	$20.3008	$20.30	$20.30	$20.30
Purchase #6	$42.98	6.499%	$45.7733	$45.77	$45.75	$45.80
Purchase #7	$19.38	11.458%	$21.6006	$21.60	$21.60	$21.60
7 purchase totals =	$528.18		$571.4401	$571.43	$571.40	$571.50