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	$98.85	11.706%	$110.4214	$110.42	$110.40	$110.40
Purchase #2	$71.79	7.478%	$77.1585	$77.16	$77.15	$77.20
Purchase #3	$109.68	12.661%	$123.5666	$123.57	$123.55	$123.60
Purchase #4	$170.60	5.737%	$180.3873	$180.39	$180.40	$180.40
Purchase #5	$81.87	9.187%	$89.3914	$89.39	$89.40	$89.40
Purchase #6	$135.76	11.606%	$151.5163	$151.52	$151.50	$151.50
Purchase #7	$111.73	5.209%	$117.55	$117.55	$117.55	$117.60
7 purchase totals =	$780.28		$849.9915	$850.00	$849.95	$850.10