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	$96.41	9.847%	$105.9035	$105.90	$105.90	$105.90
Purchase #2	$146.90	5.795%	$155.4129	$155.41	$155.40	$155.40
Purchase #3	$106.97	12.723%	$120.5798	$120.58	$120.60	$120.60
Purchase #4	$186.81	7.432%	$200.6937	$200.69	$200.70	$200.70
Purchase #5	$68.96	13.581%	$78.3255	$78.33	$78.35	$78.30
Purchase #6	$209.80	6.499%	$223.4349	$223.43	$223.45	$223.40
Purchase #7	$25.45	6.324%	$27.0595	$27.06	$27.05	$27.10
7 purchase totals =	$841.30		$911.4098	$911.40	$911.45	$911.40