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	$193.81	12.170%	$217.3967	$217.40	$217.40	$217.40
Purchase #2	$150.53	5.830%	$159.3059	$159.31	$159.30	$159.30
Purchase #3	$71.71	13.851%	$81.6426	$81.64	$81.65	$81.60
Purchase #4	$178.55	3.794%	$185.3242	$185.32	$185.30	$185.30
Purchase #5	$241.30	5.219%	$253.8934	$253.89	$253.90	$253.90
Purchase #6	$150.94	8.664%	$164.0174	$164.02	$164.00	$164.00
Purchase #7	$53.42	11.552%	$59.5911	$59.59	$59.60	$59.60
7 purchase totals =	$1,040.26		$1,121.1713	$1,121.17	$1,121.15	$1,121.10