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	$134.55	4.400%	$140.4702	$140.47	$140.45	$140.50
Purchase #2	$204.50	8.357%	$221.5901	$221.59	$221.60	$221.60
Purchase #3	$203.26	12.373%	$228.4094	$228.41	$228.40	$228.40
Purchase #4	$59.83	5.488%	$63.1135	$63.11	$63.10	$63.10
Purchase #5	$35.33	13.200%	$39.9936	$39.99	$40.00	$40.00
Purchase #6	$219.31	6.429%	$233.4094	$233.41	$233.40	$233.40
Purchase #7	$140.91	7.826%	$151.9376	$151.94	$151.95	$151.90
7 purchase totals =	$997.69		$1,078.9238	$1,078.92	$1,078.90	$1,078.90