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	$248.34	3.284%	$256.4955	$256.50	$256.50	$256.50
Purchase #2	$41.27	9.790%	$45.3103	$45.31	$45.30	$45.30
Purchase #3	$33.67	3.494%	$34.8464	$34.85	$34.85	$34.80
Purchase #4	$110.72	12.693%	$124.7737	$124.77	$124.75	$124.80
Purchase #5	$147.32	8.518%	$159.8687	$159.87	$159.85	$159.90
Purchase #6	$212.52	11.228%	$236.3817	$236.38	$236.40	$236.40
Purchase #7	$132.60	7.427%	$142.4482	$142.45	$142.45	$142.40
7 purchase totals =	$926.44		$1,000.1245	$1,000.13	$1,000.10	$1,000.10