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	$209.38	10.450%	$231.2602	$231.26	$231.25	$231.30
Purchase #2	$230.72	10.586%	$255.144	$255.14	$255.15	$255.10
Purchase #3	$111.52	7.295%	$119.6554	$119.66	$119.65	$119.70
Purchase #4	$198.33	11.770%	$221.6734	$221.67	$221.65	$221.70
Purchase #5	$74.70	5.556%	$78.8503	$78.85	$78.85	$78.90
Purchase #6	$59.30	4.422%	$61.9222	$61.92	$61.90	$61.90
Purchase #7	$47.59	10.258%	$52.4718	$52.47	$52.45	$52.50
7 purchase totals =	$931.54		$1,020.9773	$1,020.97	$1,020.90	$1,021.10