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	$6.64	8.462%	$7.2019	$7.20	$7.20	$7.20
Purchase #2	$160.27	11.543%	$178.77	$178.77	$178.75	$178.80
Purchase #3	$163.36	13.641%	$185.6439	$185.64	$185.65	$185.60
Purchase #4	$134.67	5.298%	$141.8048	$141.80	$141.80	$141.80
Purchase #5	$77.61	9.849%	$85.2538	$85.25	$85.25	$85.30
Purchase #6	$59.32	13.138%	$67.1135	$67.11	$67.10	$67.10
Purchase #7	$73.81	12.592%	$83.1042	$83.10	$83.10	$83.10
7 purchase totals =	$675.68		$748.8921	$748.87	$748.85	$748.90