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	$61.87	13.628%	$70.3016	$70.30	$70.30	$70.30
Purchase #2	$139.87	11.242%	$155.5942	$155.59	$155.60	$155.60
Purchase #3	$25.67	6.564%	$27.355	$27.36	$27.35	$27.40
Purchase #4	$219.34	9.325%	$239.7935	$239.79	$239.80	$239.80
Purchase #5	$177.72	10.638%	$196.6259	$196.63	$196.65	$196.60
Purchase #6	$138.92	8.835%	$151.1936	$151.19	$151.20	$151.20
Purchase #7	$190.27	3.754%	$197.4127	$197.41	$197.40	$197.40
7 purchase totals =	$953.66		$1,038.2765	$1,038.27	$1,038.30	$1,038.30