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	$244.94	11.665%	$273.5123	$273.51	$273.50	$273.50
Purchase #2	$65.81	11.421%	$73.3262	$73.33	$73.35	$73.30
Purchase #3	$75.69	10.834%	$83.8903	$83.89	$83.90	$83.90
Purchase #4	$69.85	13.733%	$79.4425	$79.44	$79.45	$79.40
Purchase #5	$160.86	4.169%	$167.5663	$167.57	$167.55	$167.60
Purchase #6	$59.52	3.854%	$61.8139	$61.81	$61.80	$61.80
Purchase #7	$111.57	5.357%	$117.5468	$117.55	$117.55	$117.50
7 purchase totals =	$788.24		$857.0983	$857.10	$857.10	$857.00