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	$110.75	4.788%	$116.0527	$116.05	$116.05	$116.10
Purchase #2	$78.89	12.711%	$88.9177	$88.92	$88.90	$88.90
Purchase #3	$226.69	13.820%	$258.0186	$258.02	$258.00	$258.00
Purchase #4	$28.44	12.276%	$31.9313	$31.93	$31.95	$31.90
Purchase #5	$138.72	5.697%	$146.6229	$146.62	$146.60	$146.60
Purchase #6	$153.85	4.599%	$160.9256	$160.93	$160.95	$160.90
Purchase #7	$154.52	3.499%	$159.9267	$159.93	$159.95	$159.90
7 purchase totals =	$891.86		$962.3955	$962.40	$962.40	$962.30