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	$235.81	13.553%	$267.7693	$267.77	$267.75	$267.80
Purchase #2	$59.89	9.412%	$65.5268	$65.53	$65.55	$65.50
Purchase #3	$72.98	7.458%	$78.4228	$78.42	$78.40	$78.40
Purchase #4	$41.32	12.466%	$46.471	$46.47	$46.45	$46.50
Purchase #5	$23.32	8.194%	$25.2308	$25.23	$25.25	$25.20
Purchase #6	$169.56	9.112%	$185.0103	$185.01	$185.00	$185.00
Purchase #7	$214.52	3.533%	$222.099	$222.10	$222.10	$222.10
7 purchase totals =	$817.40		$890.5300	$890.53	$890.50	$890.50