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	$71.73	9.294%	$78.3966	$78.40	$78.40	$78.40
Purchase #2	$111.57	12.406%	$125.4114	$125.41	$125.40	$125.40
Purchase #3	$124.31	12.426%	$139.7568	$139.76	$139.75	$139.80
Purchase #4	$185.76	9.647%	$203.6803	$203.68	$203.70	$203.70
Purchase #5	$133.51	4.803%	$139.9225	$139.92	$139.90	$139.90
Purchase #6	$12.38	11.420%	$13.7938	$13.79	$13.80	$13.80
Purchase #7	$107.90	6.128%	$114.5121	$114.51	$114.50	$114.50
7 purchase totals =	$747.16		$815.4735	$815.47	$815.45	$815.50