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	$103.50	6.139%	$109.8539	$109.85	$109.85	$109.90
Purchase #2	$134.72	11.709%	$150.4944	$150.49	$150.50	$150.50
Purchase #3	$174.67	12.777%	$196.9876	$196.99	$197.00	$197.00
Purchase #4	$68.51	12.632%	$77.1642	$77.16	$77.15	$77.20
Purchase #5	$150.33	8.526%	$163.1471	$163.15	$163.15	$163.10
Purchase #6	$168.37	10.126%	$185.4191	$185.42	$185.40	$185.40
Purchase #7	$138.29	10.314%	$152.5532	$152.55	$152.55	$152.60
7 purchase totals =	$938.39		$1,035.6195	$1,035.61	$1,035.60	$1,035.70