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	$136.48	10.273%	$150.5006	$150.50	$150.50	$150.50
Purchase #2	$129.47	11.342%	$144.1545	$144.15	$144.15	$144.20
Purchase #3	$211.45	7.535%	$227.3828	$227.38	$227.40	$227.40
Purchase #4	$36.67	10.509%	$40.5237	$40.52	$40.50	$40.50
Purchase #5	$247.27	11.431%	$275.5354	$275.54	$275.55	$275.50
Purchase #6	$35.61	12.259%	$39.9754	$39.98	$40.00	$40.00
Purchase #7	$67.41	4.675%	$70.5614	$70.56	$70.55	$70.60
7 purchase totals =	$864.36		$948.6338	$948.63	$948.65	$948.70