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	$72.38	8.583%	$78.5924	$78.59	$78.60	$78.60
Purchase #2	$101.62	11.581%	$113.3886	$113.39	$113.40	$113.40
Purchase #3	$93.50	7.773%	$100.7678	$100.77	$100.75	$100.80
Purchase #4	$53.63	10.739%	$59.3893	$59.39	$59.40	$59.40
Purchase #5	$38.58	7.200%	$41.3578	$41.36	$41.35	$41.40
Purchase #6	$195.31	5.572%	$206.1927	$206.19	$206.20	$206.20
Purchase #7	$156.68	12.595%	$176.4138	$176.41	$176.40	$176.40
7 purchase totals =	$711.70		$776.1024	$776.10	$776.10	$776.20