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	$23.39	12.866%	$26.3994	$26.40	$26.40	$26.40
Purchase #2	$91.82	12.580%	$103.371	$103.37	$103.35	$103.40
Purchase #3	$191.43	5.103%	$201.1987	$201.20	$201.20	$201.20
Purchase #4	$142.86	6.330%	$151.903	$151.90	$151.90	$151.90
Purchase #5	$123.59	13.800%	$140.6454	$140.65	$140.65	$140.60
Purchase #6	$242.82	5.226%	$255.5098	$255.51	$255.50	$255.50
Purchase #7	$150.60	6.183%	$159.9116	$159.91	$159.90	$159.90
7 purchase totals =	$966.51		$1,038.9389	$1,038.94	$1,038.90	$1,038.90