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	$139.60	9.173%	$152.4055	$152.41	$152.40	$152.40
Purchase #2	$24.36	13.742%	$27.7076	$27.71	$27.70	$27.70
Purchase #3	$36.70	11.273%	$40.8372	$40.84	$40.85	$40.80
Purchase #4	$150.25	5.232%	$158.1111	$158.11	$158.10	$158.10
Purchase #5	$210.93	10.713%	$233.5269	$233.53	$233.55	$233.50
Purchase #6	$114.54	11.395%	$127.5918	$127.59	$127.60	$127.60
Purchase #7	$106.46	3.724%	$110.4246	$110.42	$110.40	$110.40
7 purchase totals =	$782.84		$850.6047	$850.61	$850.60	$850.50