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	$123.25	3.517%	$127.5847	$127.58	$127.60	$127.60
Purchase #2	$212.66	7.631%	$228.8881	$228.89	$228.90	$228.90
Purchase #3	$189.72	12.402%	$213.2491	$213.25	$213.25	$213.20
Purchase #4	$140.73	9.591%	$154.2274	$154.23	$154.25	$154.20
Purchase #5	$13.95	9.278%	$15.2443	$15.24	$15.25	$15.20
Purchase #6	$234.62	12.739%	$264.5082	$264.51	$264.50	$264.50
Purchase #7	$224.82	13.519%	$255.2134	$255.21	$255.20	$255.20
7 purchase totals =	$1,139.75		$1,258.9152	$1,258.91	$1,258.95	$1,258.80