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	$107.62	13.845%	$122.52	$122.52	$122.50	$122.50
Purchase #2	$57.40	8.199%	$62.1062	$62.11	$62.10	$62.10
Purchase #3	$35.90	5.471%	$37.8641	$37.86	$37.85	$37.90
Purchase #4	$174.52	5.354%	$183.8638	$183.86	$183.85	$183.90
Purchase #5	$34.78	9.566%	$38.1071	$38.11	$38.10	$38.10
Purchase #6	$207.42	12.807%	$233.9843	$233.98	$234.00	$234.00
Purchase #7	$52.85	4.778%	$55.3752	$55.38	$55.40	$55.40
7 purchase totals =	$670.49		$733.8207	$733.82	$733.80	$733.90