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	$12.33	6.344%	$13.1122	$13.11	$13.10	$13.10
Purchase #2	$30.73	12.549%	$34.5863	$34.59	$34.60	$34.60
Purchase #3	$110.73	11.535%	$123.5027	$123.50	$123.50	$123.50
Purchase #4	$56.27	12.154%	$63.1091	$63.11	$63.10	$63.10
Purchase #5	$195.88	10.798%	$217.0311	$217.03	$217.05	$217.00
Purchase #6	$86.74	3.249%	$89.5582	$89.56	$89.55	$89.60
Purchase #7	$117.74	12.714%	$132.7095	$132.71	$132.70	$132.70
7 purchase totals =	$610.42		$673.6091	$673.61	$673.60	$673.60