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	$159.60	5.309%	$168.0732	$168.07	$168.05	$168.10
Purchase #2	$224.32	5.870%	$237.4876	$237.49	$237.50	$237.50
Purchase #3	$250.32	4.864%	$262.4956	$262.50	$262.50	$262.50
Purchase #4	$68.33	9.637%	$74.915	$74.92	$74.90	$74.90
Purchase #5	$190.68	10.711%	$211.1037	$211.10	$211.10	$211.10
Purchase #6	$68.32	6.684%	$72.8865	$72.89	$72.90	$72.90
Purchase #7	$49.95	10.367%	$55.1283	$55.13	$55.15	$55.10
7 purchase totals =	$1,011.52		$1,082.0899	$1,082.10	$1,082.10	$1,082.10