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	$34.30	9.610%	$37.5962	$37.60	$37.60	$37.60
Purchase #2	$19.28	7.206%	$20.6693	$20.67	$20.65	$20.70
Purchase #3	$250.87	7.446%	$269.5498	$269.55	$269.55	$269.50
Purchase #4	$178.96	9.594%	$196.1294	$196.13	$196.15	$196.10
Purchase #5	$155.61	6.138%	$165.1613	$165.16	$165.15	$165.20
Purchase #6	$74.80	13.656%	$85.0147	$85.01	$85.00	$85.00
Purchase #7	$181.67	5.453%	$191.5765	$191.58	$191.60	$191.60
7 purchase totals =	$895.49		$965.6972	$965.70	$965.70	$965.70