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	$18.93	12.135%	$21.2272	$21.23	$21.25	$21.20
Purchase #2	$242.71	8.611%	$263.6098	$263.61	$263.60	$263.60
Purchase #3	$199.73	11.854%	$223.406	$223.41	$223.40	$223.40
Purchase #4	$84.79	5.660%	$89.5891	$89.59	$89.60	$89.60
Purchase #5	$17.29	3.344%	$17.8682	$17.87	$17.85	$17.90
Purchase #6	$51.29	11.615%	$57.2473	$57.25	$57.25	$57.20
Purchase #7	$101.43	11.711%	$113.3085	$113.31	$113.30	$113.30
7 purchase totals =	$716.17		$786.2561	$786.27	$786.25	$786.20