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	$109.58	13.814%	$124.7174	$124.72	$124.70	$124.70
Purchase #2	$224.71	7.270%	$241.0464	$241.05	$241.05	$241.00
Purchase #3	$30.42	10.843%	$33.7184	$33.72	$33.70	$33.70
Purchase #4	$184.34	13.707%	$209.6075	$209.61	$209.60	$209.60
Purchase #5	$181.37	6.808%	$193.7177	$193.72	$193.70	$193.70
Purchase #6	$85.90	5.845%	$90.9209	$90.92	$90.90	$90.90
Purchase #7	$217.92	9.155%	$237.8706	$237.87	$237.85	$237.90
7 purchase totals =	$1,034.24		$1,131.5989	$1,131.61	$1,131.50	$1,131.50