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	$75.49	6.120%	$80.11	$80.11	$80.10	$80.10
Purchase #2	$138.60	12.274%	$155.6118	$155.61	$155.60	$155.60
Purchase #3	$80.72	9.418%	$88.3222	$88.32	$88.30	$88.30
Purchase #4	$91.94	9.772%	$100.9244	$100.92	$100.90	$100.90
Purchase #5	$221.78	13.839%	$252.4721	$252.47	$252.45	$252.50
Purchase #6	$159.69	5.139%	$167.8965	$167.90	$167.90	$167.90
Purchase #7	$205.60	3.383%	$212.5554	$212.56	$212.55	$212.60
7 purchase totals =	$973.82		$1,057.8924	$1,057.89	$1,057.80	$1,057.90