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	$19.57	7.648%	$21.0667	$21.07	$21.05	$21.10
Purchase #2	$88.50	4.290%	$92.2967	$92.30	$92.30	$92.30
Purchase #3	$183.56	12.167%	$205.8937	$205.89	$205.90	$205.90
Purchase #4	$81.97	3.798%	$85.0832	$85.08	$85.10	$85.10
Purchase #5	$180.91	8.383%	$196.0757	$196.08	$196.10	$196.10
Purchase #6	$172.30	13.517%	$195.5898	$195.59	$195.60	$195.60
Purchase #7	$193.94	9.156%	$211.6971	$211.70	$211.70	$211.70
7 purchase totals =	$920.75		$1,007.7029	$1,007.71	$1,007.75	$1,007.80