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	$227.79	3.706%	$236.2319	$236.23	$236.25	$236.20
Purchase #2	$228.86	5.706%	$241.9188	$241.92	$241.90	$241.90
Purchase #3	$147.79	6.343%	$157.1643	$157.16	$157.15	$157.20
Purchase #4	$131.46	11.526%	$146.6121	$146.61	$146.60	$146.60
Purchase #5	$47.97	13.436%	$54.4152	$54.42	$54.40	$54.40
Purchase #6	$105.78	3.639%	$109.6293	$109.63	$109.65	$109.60
Purchase #7	$56.57	5.104%	$59.4573	$59.46	$59.45	$59.50
7 purchase totals =	$946.22		$1,005.4289	$1,005.43	$1,005.40	$1,005.40