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	$226.83	12.778%	$255.8143	$255.81	$255.80	$255.80
Purchase #2	$84.50	11.382%	$94.1178	$94.12	$94.10	$94.10
Purchase #3	$48.48	7.535%	$52.133	$52.13	$52.15	$52.10
Purchase #4	$75.52	3.853%	$78.4298	$78.43	$78.45	$78.40
Purchase #5	$15.54	4.369%	$16.2189	$16.22	$16.20	$16.20
Purchase #6	$23.90	9.132%	$26.0825	$26.08	$26.10	$26.10
Purchase #7	$91.27	9.373%	$99.8247	$99.82	$99.80	$99.80
7 purchase totals =	$566.04		$622.6210	$622.61	$622.60	$622.50