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	$229.90	8.818%	$250.1726	$250.17	$250.15	$250.20
Purchase #2	$81.71	7.787%	$88.0728	$88.07	$88.05	$88.10
Purchase #3	$94.80	13.691%	$107.7791	$107.78	$107.80	$107.80
Purchase #4	$35.40	6.839%	$37.821	$37.82	$37.80	$37.80
Purchase #5	$81.56	5.167%	$85.7742	$85.77	$85.75	$85.80
Purchase #6	$208.59	5.317%	$219.6807	$219.68	$219.70	$219.70
Purchase #7	$114.45	11.296%	$127.3783	$127.38	$127.40	$127.40
7 purchase totals =	$846.41		$916.6787	$916.67	$916.65	$916.80