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	$67.49	13.803%	$76.8056	$76.81	$76.80	$76.80
Purchase #2	$242.58	9.162%	$264.8052	$264.81	$264.80	$264.80
Purchase #3	$103.83	4.255%	$108.248	$108.25	$108.25	$108.20
Purchase #4	$114.46	12.631%	$128.9174	$128.92	$128.90	$128.90
Purchase #5	$80.46	5.818%	$85.1412	$85.14	$85.15	$85.10
Purchase #6	$86.50	11.105%	$96.1058	$96.11	$96.10	$96.10
Purchase #7	$38.59	13.133%	$43.658	$43.66	$43.65	$43.70
7 purchase totals =	$733.91		$803.6812	$803.70	$803.65	$803.60