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	$7.36	5.681%	$7.7781	$7.78	$7.80	$7.80
Purchase #2	$167.46	3.636%	$173.5488	$173.55	$173.55	$173.50
Purchase #3	$161.69	7.260%	$173.4287	$173.43	$173.45	$173.40
Purchase #4	$91.57	7.344%	$98.2949	$98.29	$98.30	$98.30
Purchase #5	$33.80	13.606%	$38.3988	$38.40	$38.40	$38.40
Purchase #6	$122.25	4.201%	$127.3857	$127.39	$127.40	$127.40
Purchase #7	$224.55	11.470%	$250.3059	$250.31	$250.30	$250.30
7 purchase totals =	$808.68		$869.1409	$869.15	$869.20	$869.10