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	$112.84	13.351%	$127.9053	$127.91	$127.90	$127.90
Purchase #2	$118.44	9.550%	$129.751	$129.75	$129.75	$129.80
Purchase #3	$65.45	4.141%	$68.1603	$68.16	$68.15	$68.20
Purchase #4	$163.71	13.557%	$185.9042	$185.90	$185.90	$185.90
Purchase #5	$70.34	11.687%	$78.5606	$78.56	$78.55	$78.60
Purchase #6	$83.80	8.429%	$90.8635	$90.86	$90.85	$90.90
Purchase #7	$62.78	8.388%	$68.046	$68.05	$68.05	$68.00
7 purchase totals =	$677.36		$749.1909	$749.19	$749.15	$749.30