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	$224.90	13.819%	$255.9789	$255.98	$256.00	$256.00
Purchase #2	$203.71	9.223%	$222.4982	$222.50	$222.50	$222.50
Purchase #3	$222.81	11.730%	$248.9456	$248.95	$248.95	$248.90
Purchase #4	$123.89	3.574%	$128.3178	$128.32	$128.30	$128.30
Purchase #5	$115.72	11.237%	$128.7235	$128.72	$128.70	$128.70
Purchase #6	$135.68	7.648%	$146.0568	$146.06	$146.05	$146.10
Purchase #7	$56.96	12.445%	$64.0487	$64.05	$64.05	$64.00
7 purchase totals =	$1,083.67		$1,194.5695	$1,194.58	$1,194.55	$1,194.50