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	$79.70	13.724%	$90.638	$90.64	$90.65	$90.60
Purchase #2	$152.35	12.542%	$171.4577	$171.46	$171.45	$171.50
Purchase #3	$8.40	8.810%	$9.14	$9.14	$9.15	$9.10
Purchase #4	$61.84	6.578%	$65.9078	$65.91	$65.90	$65.90
Purchase #5	$32.44	7.474%	$34.8646	$34.86	$34.85	$34.90
Purchase #6	$173.89	10.251%	$191.7155	$191.72	$191.70	$191.70
Purchase #7	$26.31	13.592%	$29.8861	$29.89	$29.90	$29.90
7 purchase totals =	$534.93		$593.6097	$593.62	$593.60	$593.60