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	$155.60	10.263%	$171.5692	$171.57	$171.55	$171.60
Purchase #2	$199.43	12.595%	$224.5482	$224.55	$224.55	$224.50
Purchase #3	$48.85	3.542%	$50.5803	$50.58	$50.60	$50.60
Purchase #4	$89.89	5.169%	$94.5364	$94.54	$94.55	$94.50
Purchase #5	$54.57	5.364%	$57.4971	$57.50	$57.50	$57.50
Purchase #6	$148.64	12.450%	$167.1457	$167.15	$167.15	$167.10
Purchase #7	$114.78	9.336%	$125.4959	$125.50	$125.50	$125.50
7 purchase totals =	$811.76		$891.3728	$891.39	$891.40	$891.30