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	$29.33	9.644%	$32.1586	$32.16	$32.15	$32.20
Purchase #2	$127.88	9.234%	$139.6884	$139.69	$139.70	$139.70
Purchase #3	$125.67	4.616%	$131.4709	$131.47	$131.45	$131.50
Purchase #4	$90.55	4.429%	$94.5605	$94.56	$94.55	$94.60
Purchase #5	$214.73	9.153%	$234.3842	$234.38	$234.40	$234.40
Purchase #6	$55.56	6.515%	$59.1797	$59.18	$59.20	$59.20
Purchase #7	$112.60	3.604%	$116.6581	$116.66	$116.65	$116.70
7 purchase totals =	$756.32		$808.1004	$808.10	$808.10	$808.30