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	$40.54	11.594%	$45.2402	$45.24	$45.25	$45.20
Purchase #2	$122.91	3.384%	$127.0693	$127.07	$127.05	$127.10
Purchase #3	$54.69	9.345%	$59.8008	$59.80	$59.80	$59.80
Purchase #4	$122.46	13.556%	$139.0607	$139.06	$139.05	$139.10
Purchase #5	$249.48	11.624%	$278.4796	$278.48	$278.50	$278.50
Purchase #6	$24.27	3.636%	$25.1525	$25.15	$25.15	$25.20
Purchase #7	$139.60	3.498%	$144.4832	$144.48	$144.50	$144.50
7 purchase totals =	$753.95		$819.2863	$819.28	$819.30	$819.40