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	$236.81	5.185%	$249.0886	$249.09	$249.10	$249.10
Purchase #2	$175.76	3.847%	$182.5215	$182.52	$182.50	$182.50
Purchase #3	$33.41	8.468%	$36.2392	$36.24	$36.25	$36.20
Purchase #4	$178.65	10.177%	$196.8312	$196.83	$196.85	$196.80
Purchase #5	$106.61	3.758%	$110.6164	$110.62	$110.60	$110.60
Purchase #6	$105.31	11.798%	$117.7345	$117.73	$117.75	$117.70
Purchase #7	$74.79	11.654%	$83.506	$83.51	$83.50	$83.50
7 purchase totals =	$911.34		$976.5374	$976.54	$976.55	$976.40