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	$97.80	6.126%	$103.7912	$103.79	$103.80	$103.80
Purchase #2	$79.27	13.597%	$90.0483	$90.05	$90.05	$90.00
Purchase #3	$143.30	8.783%	$155.886	$155.89	$155.90	$155.90
Purchase #4	$15.54	6.136%	$16.4935	$16.49	$16.50	$16.50
Purchase #5	$144.30	13.721%	$164.0994	$164.10	$164.10	$164.10
Purchase #6	$59.77	9.709%	$65.5731	$65.57	$65.55	$65.60
Purchase #7	$147.27	8.213%	$159.3653	$159.37	$159.35	$159.40
7 purchase totals =	$687.25		$755.2568	$755.26	$755.25	$755.30