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	$92.68	12.123%	$103.9156	$103.92	$103.90	$103.90
Purchase #2	$138.60	10.164%	$152.6873	$152.69	$152.70	$152.70
Purchase #3	$139.27	6.665%	$148.5523	$148.55	$148.55	$148.60
Purchase #4	$74.74	7.838%	$80.5981	$80.60	$80.60	$80.60
Purchase #5	$229.57	13.525%	$260.6193	$260.62	$260.60	$260.60
Purchase #6	$144.62	7.332%	$155.2235	$155.22	$155.20	$155.20
Purchase #7	$197.26	5.591%	$208.2888	$208.29	$208.30	$208.30
7 purchase totals =	$1,016.74		$1,109.8849	$1,109.89	$1,109.85	$1,109.90