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	$247.43	8.514%	$268.4962	$268.50	$268.50	$268.50
Purchase #2	$109.94	5.771%	$116.2846	$116.28	$116.30	$116.30
Purchase #3	$185.52	4.183%	$193.2803	$193.28	$193.30	$193.30
Purchase #4	$80.85	10.806%	$89.5867	$89.59	$89.60	$89.60
Purchase #5	$182.79	7.374%	$196.2689	$196.27	$196.25	$196.30
Purchase #6	$181.36	4.809%	$190.0816	$190.08	$190.10	$190.10
Purchase #7	$208.91	13.765%	$237.6665	$237.67	$237.65	$237.70
7 purchase totals =	$1,196.80		$1,291.6648	$1,291.67	$1,291.70	$1,291.80