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	$39.55	5.871%	$41.872	$41.87	$41.85	$41.90
Purchase #2	$216.77	6.233%	$230.2813	$230.28	$230.30	$230.30
Purchase #3	$96.67	5.747%	$102.2256	$102.23	$102.25	$102.20
Purchase #4	$189.94	11.565%	$211.9066	$211.91	$211.90	$211.90
Purchase #5	$117.69	13.351%	$133.4028	$133.40	$133.40	$133.40
Purchase #6	$237.31	7.577%	$255.291	$255.29	$255.30	$255.30
Purchase #7	$40.97	13.538%	$46.5165	$46.52	$46.50	$46.50
7 purchase totals =	$938.90		$1,021.4958	$1,021.50	$1,021.50	$1,021.50