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	$7.53	3.768%	$7.8137	$7.81	$7.80	$7.80
Purchase #2	$218.67	11.436%	$243.6771	$243.68	$243.70	$243.70
Purchase #3	$206.52	7.531%	$222.073	$222.07	$222.05	$222.10
Purchase #4	$244.68	4.798%	$256.4197	$256.42	$256.40	$256.40
Purchase #5	$6.89	13.255%	$7.8033	$7.80	$7.80	$7.80
Purchase #6	$186.90	4.578%	$195.4563	$195.46	$195.45	$195.50
Purchase #7	$71.77	5.654%	$75.8279	$75.83	$75.85	$75.80
7 purchase totals =	$942.96		$1,009.0710	$1,009.07	$1,009.05	$1,009.10