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	$24.88	10.440%	$27.4775	$27.48	$27.50	$27.50
Purchase #2	$241.74	7.754%	$260.4845	$260.48	$260.50	$260.50
Purchase #3	$39.90	6.213%	$42.379	$42.38	$42.40	$42.40
Purchase #4	$114.89	8.204%	$124.3156	$124.32	$124.30	$124.30
Purchase #5	$208.91	10.796%	$231.4639	$231.46	$231.45	$231.50
Purchase #6	$203.42	7.251%	$218.17	$218.17	$218.15	$218.20
Purchase #7	$79.47	7.525%	$85.4501	$85.45	$85.45	$85.50
7 purchase totals =	$913.21		$989.7406	$989.74	$989.75	$989.90