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	$111.74	10.696%	$123.6917	$123.69	$123.70	$123.70
Purchase #2	$102.98	9.819%	$113.0916	$113.09	$113.10	$113.10
Purchase #3	$212.43	10.565%	$234.8732	$234.87	$234.85	$234.90
Purchase #4	$171.67	10.675%	$189.9958	$190.00	$190.00	$190.00
Purchase #5	$35.71	9.557%	$39.1228	$39.12	$39.10	$39.10
Purchase #6	$42.27	11.500%	$47.1311	$47.13	$47.15	$47.10
Purchase #7	$127.45	12.186%	$142.9811	$142.98	$143.00	$143.00
7 purchase totals =	$804.25		$890.8873	$890.88	$890.90	$890.90