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	$10.68	5.230%	$11.2386	$11.24	$11.25	$11.20
Purchase #2	$54.95	6.589%	$58.5707	$58.57	$58.55	$58.60
Purchase #3	$249.90	4.594%	$261.3804	$261.38	$261.40	$261.40
Purchase #4	$35.57	9.485%	$38.9438	$38.94	$38.95	$38.90
Purchase #5	$94.80	10.167%	$104.4383	$104.44	$104.45	$104.40
Purchase #6	$34.54	9.660%	$37.8766	$37.88	$37.90	$37.90
Purchase #7	$82.95	7.142%	$88.8743	$88.87	$88.85	$88.90
7 purchase totals =	$563.39		$601.3227	$601.32	$601.35	$601.30