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	$95.89	3.623%	$99.3641	$99.36	$99.35	$99.40
Purchase #2	$13.33	7.109%	$14.2776	$14.28	$14.30	$14.30
Purchase #3	$128.32	6.643%	$136.8443	$136.84	$136.85	$136.80
Purchase #4	$47.78	10.262%	$52.6832	$52.68	$52.70	$52.70
Purchase #5	$16.29	12.256%	$18.2865	$18.29	$18.30	$18.30
Purchase #6	$106.25	3.615%	$110.0909	$110.09	$110.10	$110.10
Purchase #7	$108.82	13.190%	$123.1734	$123.17	$123.15	$123.20
7 purchase totals =	$516.68		$554.7200	$554.71	$554.75	$554.80