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	$28.25	11.679%	$31.5493	$31.55	$31.55	$31.50
Purchase #2	$108.29	7.385%	$116.2872	$116.29	$116.30	$116.30
Purchase #3	$58.61	12.815%	$66.1209	$66.12	$66.10	$66.10
Purchase #4	$215.50	6.374%	$229.236	$229.24	$229.25	$229.20
Purchase #5	$139.98	11.376%	$155.9041	$155.90	$155.90	$155.90
Purchase #6	$179.52	11.284%	$199.777	$199.78	$199.80	$199.80
Purchase #7	$39.57	11.346%	$44.0596	$44.06	$44.05	$44.10
7 purchase totals =	$769.72		$842.9341	$842.94	$842.95	$842.90