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	$112.82	7.177%	$120.9171	$120.92	$120.90	$120.90
Purchase #2	$242.98	13.663%	$276.1784	$276.18	$276.20	$276.20
Purchase #3	$110.72	5.539%	$116.8528	$116.85	$116.85	$116.90
Purchase #4	$86.86	13.768%	$98.8189	$98.82	$98.80	$98.80
Purchase #5	$231.93	11.161%	$257.8157	$257.82	$257.80	$257.80
Purchase #6	$237.86	7.326%	$255.2856	$255.29	$255.30	$255.30
Purchase #7	$16.72	9.433%	$18.2972	$18.30	$18.30	$18.30
7 purchase totals =	$1,039.89		$1,144.1657	$1,144.18	$1,144.15	$1,144.20