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	$99.43	9.838%	$109.2119	$109.21	$109.20	$109.20
Purchase #2	$179.92	8.534%	$195.2744	$195.27	$195.25	$195.30
Purchase #3	$198.63	10.296%	$219.0809	$219.08	$219.10	$219.10
Purchase #4	$16.25	13.611%	$18.4618	$18.46	$18.45	$18.50
Purchase #5	$71.45	13.830%	$81.3315	$81.33	$81.35	$81.30
Purchase #6	$168.30	3.284%	$173.827	$173.83	$173.85	$173.80
Purchase #7	$124.25	5.810%	$131.4689	$131.47	$131.45	$131.50
7 purchase totals =	$858.23		$928.6564	$928.65	$928.65	$928.70