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	$147.85	13.632%	$168.0049	$168.00	$168.00	$168.00
Purchase #2	$237.87	9.466%	$260.3868	$260.39	$260.40	$260.40
Purchase #3	$119.94	11.520%	$133.7571	$133.76	$133.75	$133.80
Purchase #4	$241.79	3.649%	$250.6129	$250.61	$250.60	$250.60
Purchase #5	$20.90	4.733%	$21.8892	$21.89	$21.90	$21.90
Purchase #6	$129.56	8.704%	$140.8369	$140.84	$140.85	$140.80
Purchase #7	$117.85	6.437%	$125.436	$125.44	$125.45	$125.40
7 purchase totals =	$1,015.76		$1,100.9238	$1,100.93	$1,100.95	$1,100.90