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	$244.61	13.823%	$278.4224	$278.42	$278.40	$278.40
Purchase #2	$62.90	10.745%	$69.6586	$69.66	$69.65	$69.70
Purchase #3	$246.45	13.630%	$280.0411	$280.04	$280.05	$280.00
Purchase #4	$147.27	13.336%	$166.9099	$166.91	$166.90	$166.90
Purchase #5	$75.88	3.500%	$78.5358	$78.54	$78.55	$78.50
Purchase #6	$201.27	7.278%	$215.9184	$215.92	$215.90	$215.90
Purchase #7	$91.69	8.538%	$99.5185	$99.52	$99.50	$99.50
7 purchase totals =	$1,070.07		$1,189.0047	$1,189.01	$1,188.95	$1,188.90