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	$5.97	7.331%	$6.4077	$6.41	$6.40	$6.40
Purchase #2	$172.87	10.151%	$190.418	$190.42	$190.40	$190.40
Purchase #3	$171.48	6.105%	$181.9489	$181.95	$181.95	$181.90
Purchase #4	$207.53	11.539%	$231.4769	$231.48	$231.50	$231.50
Purchase #5	$166.77	10.144%	$183.6871	$183.69	$183.70	$183.70
Purchase #6	$50.73	12.572%	$57.1078	$57.11	$57.10	$57.10
Purchase #7	$144.36	4.862%	$151.3788	$151.38	$151.40	$151.40
7 purchase totals =	$919.71		$1,002.4252	$1,002.44	$1,002.45	$1,002.40