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	$199.96	4.118%	$208.1944	$208.19	$208.20	$208.20
Purchase #2	$171.35	11.830%	$191.6207	$191.62	$191.60	$191.60
Purchase #3	$104.89	7.608%	$112.87	$112.87	$112.85	$112.90
Purchase #4	$184.86	5.221%	$194.5115	$194.51	$194.50	$194.50
Purchase #5	$89.89	9.489%	$98.4197	$98.42	$98.40	$98.40
Purchase #6	$63.84	9.788%	$70.0887	$70.09	$70.10	$70.10
Purchase #7	$32.90	13.376%	$37.3007	$37.30	$37.30	$37.30
7 purchase totals =	$847.69		$913.0057	$913.00	$912.95	$913.00