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	$33.57	12.585%	$37.7948	$37.79	$37.80	$37.80
Purchase #2	$107.80	5.177%	$113.3808	$113.38	$113.40	$113.40
Purchase #3	$183.55	8.859%	$199.8107	$199.81	$199.80	$199.80
Purchase #4	$115.58	13.355%	$131.0157	$131.02	$131.00	$131.00
Purchase #5	$112.72	4.737%	$118.0595	$118.06	$118.05	$118.10
Purchase #6	$107.94	3.725%	$111.9608	$111.96	$111.95	$112.00
Purchase #7	$137.75	9.541%	$150.8927	$150.89	$150.90	$150.90
7 purchase totals =	$798.91		$862.9150	$862.91	$862.90	$863.00