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	$106.38	12.340%	$119.5073	$119.51	$119.50	$119.50
Purchase #2	$89.49	13.209%	$101.3107	$101.31	$101.30	$101.30
Purchase #3	$147.48	13.526%	$167.4281	$167.43	$167.45	$167.40
Purchase #4	$17.29	12.386%	$19.4315	$19.43	$19.45	$19.40
Purchase #5	$166.97	9.427%	$182.7103	$182.71	$182.70	$182.70
Purchase #6	$80.58	10.746%	$89.2391	$89.24	$89.25	$89.20
Purchase #7	$157.28	6.381%	$167.316	$167.32	$167.30	$167.30
7 purchase totals =	$765.47		$846.9430	$846.95	$846.95	$846.80