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	$32.37	10.600%	$35.8012	$35.80	$35.80	$35.80
Purchase #2	$14.47	6.325%	$15.3852	$15.39	$15.40	$15.40
Purchase #3	$207.78	7.578%	$223.5256	$223.53	$223.55	$223.50
Purchase #4	$29.71	8.523%	$32.2422	$32.24	$32.25	$32.20
Purchase #5	$152.76	8.682%	$166.0226	$166.02	$166.00	$166.00
Purchase #6	$61.83	9.720%	$67.8399	$67.84	$67.85	$67.80
Purchase #7	$44.56	13.857%	$50.7347	$50.73	$50.75	$50.70
7 purchase totals =	$543.48		$591.5514	$591.55	$591.60	$591.40