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	$69.82	12.145%	$78.2996	$78.30	$78.30	$78.30
Purchase #2	$203.70	7.654%	$219.2912	$219.29	$219.30	$219.30
Purchase #3	$16.38	10.770%	$18.1441	$18.14	$18.15	$18.10
Purchase #4	$51.57	8.167%	$55.7817	$55.78	$55.80	$55.80
Purchase #5	$183.92	6.721%	$196.2813	$196.28	$196.30	$196.30
Purchase #6	$131.86	9.472%	$144.3498	$144.35	$144.35	$144.30
Purchase #7	$162.95	12.202%	$182.8332	$182.83	$182.85	$182.80
7 purchase totals =	$820.20		$894.9809	$894.97	$895.05	$894.90