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	$118.37	4.420%	$123.602	$123.60	$123.60	$123.60
Purchase #2	$232.60	8.688%	$252.8083	$252.81	$252.80	$252.80
Purchase #3	$37.63	6.446%	$40.0556	$40.06	$40.05	$40.10
Purchase #4	$156.51	11.468%	$174.4586	$174.46	$174.45	$174.50
Purchase #5	$233.44	6.861%	$249.4563	$249.46	$249.45	$249.50
Purchase #6	$156.69	6.807%	$167.3559	$167.36	$167.35	$167.40
Purchase #7	$76.58	5.180%	$80.5468	$80.55	$80.55	$80.50
7 purchase totals =	$1,011.82		$1,088.2835	$1,088.30	$1,088.25	$1,088.40