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	$156.63	10.801%	$173.5476	$173.55	$173.55	$173.50
Purchase #2	$37.93	4.648%	$39.693	$39.69	$39.70	$39.70
Purchase #3	$142.92	7.560%	$153.7248	$153.72	$153.70	$153.70
Purchase #4	$115.55	6.528%	$123.0931	$123.09	$123.10	$123.10
Purchase #5	$38.27	9.761%	$42.0055	$42.01	$42.00	$42.00
Purchase #6	$235.29	4.227%	$245.2357	$245.24	$245.25	$245.20
Purchase #7	$25.62	11.691%	$28.6152	$28.62	$28.60	$28.60
7 purchase totals =	$752.21		$805.9149	$805.92	$805.90	$805.80