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	$176.34	9.665%	$193.3833	$193.38	$193.40	$193.40
Purchase #2	$170.94	6.555%	$182.1451	$182.15	$182.15	$182.10
Purchase #3	$29.52	6.666%	$31.4878	$31.49	$31.50	$31.50
Purchase #4	$46.57	6.498%	$49.5961	$49.60	$49.60	$49.60
Purchase #5	$122.44	8.206%	$132.4874	$132.49	$132.50	$132.50
Purchase #6	$105.46	6.106%	$111.8994	$111.90	$111.90	$111.90
Purchase #7	$129.84	11.530%	$144.8106	$144.81	$144.80	$144.80
7 purchase totals =	$781.11		$845.8097	$845.82	$845.85	$845.80