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	$187.49	8.387%	$203.2148	$203.21	$203.20	$203.20
Purchase #2	$134.60	7.205%	$144.2979	$144.30	$144.30	$144.30
Purchase #3	$164.95	3.440%	$170.6243	$170.62	$170.60	$170.60
Purchase #4	$11.60	5.285%	$12.2131	$12.21	$12.20	$12.20
Purchase #5	$204.31	9.412%	$223.5397	$223.54	$223.55	$223.50
Purchase #6	$173.53	13.397%	$196.7778	$196.78	$196.80	$196.80
Purchase #7	$83.55	6.822%	$89.2498	$89.25	$89.25	$89.20
7 purchase totals =	$960.03		$1,039.9174	$1,039.91	$1,039.90	$1,039.80