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	$151.27	8.432%	$164.0251	$164.03	$164.05	$164.00
Purchase #2	$100.92	7.695%	$108.6858	$108.69	$108.70	$108.70
Purchase #3	$149.73	6.241%	$159.0746	$159.07	$159.05	$159.10
Purchase #4	$18.82	9.115%	$20.5354	$20.54	$20.55	$20.50
Purchase #5	$217.46	9.724%	$238.6058	$238.61	$238.60	$238.60
Purchase #6	$19.59	3.311%	$20.2386	$20.24	$20.25	$20.20
Purchase #7	$91.38	8.698%	$99.3282	$99.33	$99.35	$99.30
7 purchase totals =	$749.17		$810.4935	$810.51	$810.55	$810.40