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	$239.83	4.445%	$250.4904	$250.49	$250.50	$250.50
Purchase #2	$206.32	10.637%	$228.2663	$228.27	$228.25	$228.30
Purchase #3	$181.27	7.752%	$195.3221	$195.32	$195.30	$195.30
Purchase #4	$243.27	5.325%	$256.2241	$256.22	$256.20	$256.20
Purchase #5	$221.37	3.796%	$229.7732	$229.77	$229.75	$229.80
Purchase #6	$41.25	5.321%	$43.4449	$43.44	$43.45	$43.40
Purchase #7	$136.68	13.837%	$155.5924	$155.59	$155.60	$155.60
7 purchase totals =	$1,269.99		$1,359.1134	$1,359.10	$1,359.05	$1,359.10