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	$40.52	12.173%	$45.4525	$45.45	$45.45	$45.50
Purchase #2	$13.67	10.808%	$15.1475	$15.15	$15.15	$15.10
Purchase #3	$176.88	5.365%	$186.3696	$186.37	$186.35	$186.40
Purchase #4	$69.90	12.501%	$78.6382	$78.64	$78.65	$78.60
Purchase #5	$29.65	7.621%	$31.9096	$31.91	$31.90	$31.90
Purchase #6	$45.94	4.216%	$47.8768	$47.88	$47.90	$47.90
Purchase #7	$173.25	3.274%	$178.9222	$178.92	$178.90	$178.90
7 purchase totals =	$549.81		$584.3164	$584.32	$584.30	$584.30