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	$21.27	3.161%	$21.9423	$21.94	$21.95	$21.90
Purchase #2	$67.97	6.253%	$72.2202	$72.22	$72.20	$72.20
Purchase #3	$235.58	10.666%	$260.707	$260.71	$260.70	$260.70
Purchase #4	$17.79	12.418%	$19.9992	$20.00	$20.00	$20.00
Purchase #5	$54.57	8.410%	$59.1593	$59.16	$59.15	$59.20
Purchase #6	$190.40	4.267%	$198.5244	$198.52	$198.50	$198.50
Purchase #7	$127.43	12.847%	$143.8009	$143.80	$143.80	$143.80
7 purchase totals =	$715.01		$776.3533	$776.35	$776.30	$776.30