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	$247.89	9.176%	$270.6364	$270.64	$270.65	$270.60
Purchase #2	$135.80	6.564%	$144.7139	$144.71	$144.70	$144.70
Purchase #3	$134.67	6.126%	$142.9199	$142.92	$142.90	$142.90
Purchase #4	$76.30	3.408%	$78.9003	$78.90	$78.90	$78.90
Purchase #5	$111.44	10.623%	$123.2783	$123.28	$123.30	$123.30
Purchase #6	$181.41	5.262%	$190.9558	$190.96	$190.95	$191.00
Purchase #7	$120.35	10.673%	$133.195	$133.20	$133.20	$133.20
7 purchase totals =	$1,007.86		$1,084.5996	$1,084.61	$1,084.60	$1,084.60