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	$163.35	13.485%	$185.3777	$185.38	$185.40	$185.40
Purchase #2	$36.91	7.367%	$39.6292	$39.63	$39.65	$39.60
Purchase #3	$18.99	5.335%	$20.0031	$20.00	$20.00	$20.00
Purchase #4	$154.92	7.567%	$166.6428	$166.64	$166.65	$166.60
Purchase #5	$59.36	5.323%	$62.5197	$62.52	$62.50	$62.50
Purchase #6	$94.55	4.623%	$98.921	$98.92	$98.90	$98.90
Purchase #7	$61.55	10.117%	$67.777	$67.78	$67.80	$67.80
7 purchase totals =	$589.63		$640.8705	$640.87	$640.90	$640.80