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	$193.77	7.611%	$208.5178	$208.52	$208.50	$208.50
Purchase #2	$142.33	4.681%	$148.9925	$148.99	$149.00	$149.00
Purchase #3	$99.58	7.493%	$107.0415	$107.04	$107.05	$107.00
Purchase #4	$175.28	8.583%	$190.3243	$190.32	$190.30	$190.30
Purchase #5	$107.82	6.517%	$114.8466	$114.85	$114.85	$114.80
Purchase #6	$52.70	12.751%	$59.4198	$59.42	$59.40	$59.40
Purchase #7	$122.32	4.529%	$127.8599	$127.86	$127.85	$127.90
7 purchase totals =	$893.80		$957.0024	$957.00	$956.95	$956.90