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	$225.57	7.493%	$242.472	$242.47	$242.45	$242.50
Purchase #2	$129.83	11.162%	$144.3216	$144.32	$144.30	$144.30
Purchase #3	$243.99	12.150%	$273.6348	$273.63	$273.65	$273.60
Purchase #4	$177.27	10.720%	$196.2733	$196.27	$196.25	$196.30
Purchase #5	$42.86	7.106%	$45.9056	$45.91	$45.90	$45.90
Purchase #6	$60.87	9.191%	$66.4646	$66.46	$66.45	$66.50
Purchase #7	$123.73	6.195%	$131.3951	$131.40	$131.40	$131.40
7 purchase totals =	$1,004.12		$1,100.4670	$1,100.46	$1,100.40	$1,100.50