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	$249.64	3.411%	$258.1552	$258.16	$258.15	$258.20
Purchase #2	$40.77	5.642%	$43.0702	$43.07	$43.05	$43.10
Purchase #3	$196.32	6.679%	$209.4322	$209.43	$209.45	$209.40
Purchase #4	$46.82	7.846%	$50.4935	$50.49	$50.50	$50.50
Purchase #5	$169.65	8.190%	$183.5443	$183.54	$183.55	$183.50
Purchase #6	$244.58	7.787%	$263.6254	$263.63	$263.65	$263.60
Purchase #7	$65.29	10.549%	$72.1774	$72.18	$72.20	$72.20
7 purchase totals =	$1,013.07		$1,080.4982	$1,080.50	$1,080.55	$1,080.50