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	$212.52	12.589%	$239.2741	$239.27	$239.25	$239.30
Purchase #2	$110.43	9.306%	$120.7066	$120.71	$120.70	$120.70
Purchase #3	$85.30	5.253%	$89.7808	$89.78	$89.80	$89.80
Purchase #4	$6.85	7.803%	$7.3845	$7.38	$7.40	$7.40
Purchase #5	$103.75	10.355%	$114.4933	$114.49	$114.50	$114.50
Purchase #6	$110.40	11.873%	$123.5078	$123.51	$123.50	$123.50
Purchase #7	$249.68	10.205%	$275.1598	$275.16	$275.15	$275.20
7 purchase totals =	$878.93		$970.3069	$970.30	$970.30	$970.40