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	$113.34	12.311%	$127.2933	$127.29	$127.30	$127.30
Purchase #2	$48.51	12.137%	$54.3977	$54.40	$54.40	$54.40
Purchase #3	$24.79	12.471%	$27.8816	$27.88	$27.90	$27.90
Purchase #4	$13.92	7.359%	$14.9444	$14.94	$14.95	$14.90
Purchase #5	$54.88	13.169%	$62.1071	$62.11	$62.10	$62.10
Purchase #6	$183.82	13.219%	$208.1192	$208.12	$208.10	$208.10
Purchase #7	$159.35	6.760%	$170.1221	$170.12	$170.10	$170.10
7 purchase totals =	$598.61		$664.8654	$664.86	$664.85	$664.80