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	$19.35	9.570%	$21.2018	$21.20	$21.20	$21.20
Purchase #2	$61.99	9.712%	$68.0105	$68.01	$68.00	$68.00
Purchase #3	$156.75	10.704%	$173.5285	$173.53	$173.55	$173.50
Purchase #4	$40.45	13.300%	$45.8299	$45.83	$45.85	$45.80
Purchase #5	$128.41	8.688%	$139.5663	$139.57	$139.55	$139.60
Purchase #6	$88.61	12.347%	$99.5507	$99.55	$99.55	$99.60
Purchase #7	$50.57	7.129%	$54.1751	$54.18	$54.20	$54.20
7 purchase totals =	$546.13		$601.8628	$601.87	$601.90	$601.90