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	$69.57	4.205%	$72.4954	$72.50	$72.50	$72.50
Purchase #2	$100.82	10.399%	$111.3043	$111.30	$111.30	$111.30
Purchase #3	$181.93	10.276%	$200.6251	$200.63	$200.65	$200.60
Purchase #4	$62.42	10.215%	$68.7962	$68.80	$68.80	$68.80
Purchase #5	$199.65	8.581%	$216.782	$216.78	$216.80	$216.80
Purchase #6	$51.31	11.136%	$57.0239	$57.02	$57.00	$57.00
Purchase #7	$128.42	8.565%	$139.4192	$139.42	$139.40	$139.40
7 purchase totals =	$794.12		$866.4461	$866.45	$866.45	$866.40