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	$37.87	7.312%	$40.6391	$40.64	$40.65	$40.60
Purchase #2	$105.60	4.758%	$110.6244	$110.62	$110.60	$110.60
Purchase #3	$117.56	4.714%	$123.1018	$123.10	$123.10	$123.10
Purchase #4	$97.83	11.654%	$109.2311	$109.23	$109.25	$109.20
Purchase #5	$231.28	6.813%	$247.0371	$247.04	$247.05	$247.00
Purchase #6	$129.56	10.799%	$143.5512	$143.55	$143.55	$143.60
Purchase #7	$76.50	4.851%	$80.211	$80.21	$80.20	$80.20
7 purchase totals =	$796.20		$854.3957	$854.39	$854.40	$854.30