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	$49.89	13.708%	$56.7289	$56.73	$56.75	$56.70
Purchase #2	$70.37	7.152%	$75.4029	$75.40	$75.40	$75.40
Purchase #3	$246.68	4.102%	$256.7988	$256.80	$256.80	$256.80
Purchase #4	$125.64	13.505%	$142.6077	$142.61	$142.60	$142.60
Purchase #5	$242.38	11.307%	$269.7859	$269.79	$269.80	$269.80
Purchase #6	$181.43	3.406%	$187.6095	$187.61	$187.60	$187.60
Purchase #7	$30.50	4.361%	$31.8301	$31.83	$31.85	$31.80
7 purchase totals =	$946.89		$1,020.7638	$1,020.77	$1,020.80	$1,020.70