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	$217.79	5.794%	$230.4088	$230.41	$230.40	$230.40
Purchase #2	$31.47	11.836%	$35.1948	$35.19	$35.20	$35.20
Purchase #3	$240.44	6.419%	$255.8738	$255.87	$255.85	$255.90
Purchase #4	$38.42	6.560%	$40.9404	$40.94	$40.95	$40.90
Purchase #5	$104.33	8.198%	$112.883	$112.88	$112.90	$112.90
Purchase #6	$97.99	5.298%	$103.1815	$103.18	$103.20	$103.20
Purchase #7	$83.54	8.234%	$90.4187	$90.42	$90.40	$90.40
7 purchase totals =	$813.98		$868.9010	$868.89	$868.90	$868.90