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	$33.77	4.257%	$35.2076	$35.21	$35.20	$35.20
Purchase #2	$74.60	4.704%	$78.1092	$78.11	$78.10	$78.10
Purchase #3	$140.27	5.762%	$148.3524	$148.35	$148.35	$148.40
Purchase #4	$37.70	10.138%	$41.522	$41.52	$41.50	$41.50
Purchase #5	$98.77	10.542%	$109.1823	$109.18	$109.20	$109.20
Purchase #6	$225.69	8.181%	$244.1537	$244.15	$244.15	$244.20
Purchase #7	$132.97	8.153%	$143.811	$143.81	$143.80	$143.80
7 purchase totals =	$743.77		$800.3382	$800.33	$800.30	$800.40