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	$149.66	12.740%	$168.7267	$168.73	$168.75	$168.70
Purchase #2	$98.51	3.584%	$102.0406	$102.04	$102.05	$102.00
Purchase #3	$165.74	12.314%	$186.1492	$186.15	$186.15	$186.10
Purchase #4	$244.27	7.495%	$262.578	$262.58	$262.60	$262.60
Purchase #5	$65.64	9.828%	$72.0911	$72.09	$72.10	$72.10
Purchase #6	$181.95	4.494%	$190.1268	$190.13	$190.15	$190.10
Purchase #7	$34.89	11.175%	$38.789	$38.79	$38.80	$38.80
7 purchase totals =	$940.66		$1,020.5014	$1,020.51	$1,020.60	$1,020.40