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	$240.68	13.650%	$273.5328	$273.53	$273.55	$273.50
Purchase #2	$116.80	9.803%	$128.2499	$128.25	$128.25	$128.20
Purchase #3	$93.30	11.399%	$103.9353	$103.94	$103.95	$103.90
Purchase #4	$142.61	13.713%	$162.1661	$162.17	$162.15	$162.20
Purchase #5	$35.37	9.482%	$38.7238	$38.72	$38.70	$38.70
Purchase #6	$230.92	9.496%	$252.8482	$252.85	$252.85	$252.80
Purchase #7	$151.83	10.583%	$167.8982	$167.90	$167.90	$167.90
7 purchase totals =	$1,011.51		$1,127.3543	$1,127.36	$1,127.35	$1,127.20