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	$100.66	10.564%	$111.2937	$111.29	$111.30	$111.30
Purchase #2	$107.92	4.633%	$112.9199	$112.92	$112.90	$112.90
Purchase #3	$72.41	5.505%	$76.3962	$76.40	$76.40	$76.40
Purchase #4	$22.61	7.786%	$24.3704	$24.37	$24.35	$24.40
Purchase #5	$145.88	4.281%	$152.1251	$152.13	$152.15	$152.10
Purchase #6	$92.44	12.192%	$103.7103	$103.71	$103.70	$103.70
Purchase #7	$210.58	11.406%	$234.5988	$234.60	$234.60	$234.60
7 purchase totals =	$752.50		$815.4144	$815.42	$815.40	$815.40