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	$76.49	4.397%	$79.8533	$79.85	$79.85	$79.90
Purchase #2	$250.51	13.577%	$284.5217	$284.52	$284.50	$284.50
Purchase #3	$224.59	11.432%	$250.2651	$250.27	$250.25	$250.30
Purchase #4	$99.87	9.532%	$109.3896	$109.39	$109.40	$109.40
Purchase #5	$101.68	7.426%	$109.2308	$109.23	$109.25	$109.20
Purchase #6	$75.37	10.773%	$83.4896	$83.49	$83.50	$83.50
Purchase #7	$87.42	9.464%	$95.6934	$95.69	$95.70	$95.70
7 purchase totals =	$915.93		$1,012.4435	$1,012.44	$1,012.45	$1,012.50