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	$223.90	4.103%	$233.0866	$233.09	$233.10	$233.10
Purchase #2	$12.53	6.190%	$13.3056	$13.31	$13.30	$13.30
Purchase #3	$188.60	10.868%	$209.097	$209.10	$209.10	$209.10
Purchase #4	$114.41	5.420%	$120.611	$120.61	$120.60	$120.60
Purchase #5	$90.86	9.546%	$99.5335	$99.53	$99.55	$99.50
Purchase #6	$14.68	12.369%	$16.4958	$16.50	$16.50	$16.50
Purchase #7	$138.47	6.241%	$147.1119	$147.11	$147.10	$147.10
7 purchase totals =	$783.45		$839.2414	$839.25	$839.25	$839.20