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	$11.92	12.857%	$13.4526	$13.45	$13.45	$13.50
Purchase #2	$248.74	6.749%	$265.5275	$265.53	$265.55	$265.50
Purchase #3	$82.70	9.192%	$90.3018	$90.30	$90.30	$90.30
Purchase #4	$154.53	7.139%	$165.5619	$165.56	$165.55	$165.60
Purchase #5	$167.65	5.152%	$176.2873	$176.29	$176.30	$176.30
Purchase #6	$87.95	3.498%	$91.0265	$91.03	$91.05	$91.00
Purchase #7	$32.97	10.564%	$36.453	$36.45	$36.45	$36.50
7 purchase totals =	$786.46		$838.6106	$838.61	$838.65	$838.70