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	$29.92	6.281%	$31.7993	$31.80	$31.80	$31.80
Purchase #2	$16.53	9.783%	$18.1471	$18.15	$18.15	$18.10
Purchase #3	$116.28	3.617%	$120.4858	$120.49	$120.50	$120.50
Purchase #4	$228.25	11.766%	$255.1059	$255.11	$255.10	$255.10
Purchase #5	$113.97	8.178%	$123.2905	$123.29	$123.30	$123.30
Purchase #6	$88.57	4.424%	$92.4883	$92.49	$92.50	$92.50
Purchase #7	$40.86	9.199%	$44.6187	$44.62	$44.60	$44.60
7 purchase totals =	$634.38		$685.9356	$685.95	$685.95	$685.90