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	$9.53	7.316%	$10.2272	$10.23	$10.25	$10.20
Purchase #2	$28.86	7.345%	$30.9798	$30.98	$31.00	$31.00
Purchase #3	$249.94	7.815%	$269.4728	$269.47	$269.45	$269.50
Purchase #4	$21.31	4.558%	$22.2813	$22.28	$22.30	$22.30
Purchase #5	$56.82	4.725%	$59.5047	$59.50	$59.50	$59.50
Purchase #6	$66.67	9.356%	$72.9076	$72.91	$72.90	$72.90
Purchase #7	$62.84	6.779%	$67.0999	$67.10	$67.10	$67.10
7 purchase totals =	$495.97		$532.4733	$532.47	$532.50	$532.50