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	$158.25	4.132%	$164.7889	$164.79	$164.80	$164.80
Purchase #2	$220.52	10.575%	$243.84	$243.84	$243.85	$243.80
Purchase #3	$27.41	12.831%	$30.927	$30.93	$30.95	$30.90
Purchase #4	$142.86	7.190%	$153.1316	$153.13	$153.15	$153.10
Purchase #5	$73.93	6.290%	$78.5802	$78.58	$78.60	$78.60
Purchase #6	$65.67	3.165%	$67.7485	$67.75	$67.75	$67.70
Purchase #7	$54.76	13.714%	$62.2698	$62.27	$62.25	$62.30
7 purchase totals =	$743.40		$801.2860	$801.29	$801.35	$801.20