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	$139.59	3.128%	$143.9564	$143.96	$143.95	$144.00
Purchase #2	$59.61	13.729%	$67.7939	$67.79	$67.80	$67.80
Purchase #3	$97.50	11.219%	$108.4385	$108.44	$108.45	$108.40
Purchase #4	$140.25	11.203%	$155.9622	$155.96	$155.95	$156.00
Purchase #5	$76.98	6.646%	$82.0961	$82.10	$82.10	$82.10
Purchase #6	$139.30	8.784%	$151.5361	$151.54	$151.55	$151.50
Purchase #7	$149.85	9.855%	$164.6177	$164.62	$164.60	$164.60
7 purchase totals =	$803.08		$874.4009	$874.41	$874.40	$874.40