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	$105.66	12.540%	$118.9098	$118.91	$118.90	$118.90
Purchase #2	$117.30	12.320%	$131.7514	$131.75	$131.75	$131.80
Purchase #3	$92.28	9.732%	$101.2607	$101.26	$101.25	$101.30
Purchase #4	$127.29	7.873%	$137.3115	$137.31	$137.30	$137.30
Purchase #5	$205.31	11.837%	$229.6125	$229.61	$229.60	$229.60
Purchase #6	$104.48	4.719%	$109.4104	$109.41	$109.40	$109.40
Purchase #7	$17.68	5.750%	$18.6966	$18.70	$18.70	$18.70
7 purchase totals =	$770.00		$846.9529	$846.95	$846.90	$847.00