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	$78.30	3.232%	$80.8307	$80.83	$80.85	$80.80
Purchase #2	$81.78	9.469%	$89.5237	$89.52	$89.50	$89.50
Purchase #3	$239.61	10.471%	$264.6996	$264.70	$264.70	$264.70
Purchase #4	$49.71	7.262%	$53.3199	$53.32	$53.30	$53.30
Purchase #5	$26.32	12.666%	$29.6537	$29.65	$29.65	$29.70
Purchase #6	$114.78	3.585%	$118.8949	$118.89	$118.90	$118.90
Purchase #7	$167.89	9.724%	$184.2156	$184.22	$184.20	$184.20
7 purchase totals =	$758.39		$821.1381	$821.13	$821.10	$821.10