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	$150.68	11.406%	$167.8666	$167.87	$167.85	$167.90
Purchase #2	$38.84	3.838%	$40.3307	$40.33	$40.35	$40.30
Purchase #3	$70.60	10.630%	$78.1048	$78.10	$78.10	$78.10
Purchase #4	$149.35	10.403%	$164.8869	$164.89	$164.90	$164.90
Purchase #5	$123.50	5.582%	$130.3938	$130.39	$130.40	$130.40
Purchase #6	$46.40	7.810%	$50.0238	$50.02	$50.00	$50.00
Purchase #7	$234.69	10.869%	$260.1985	$260.20	$260.20	$260.20
7 purchase totals =	$814.06		$891.8051	$891.80	$891.80	$891.80