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	$89.84	13.798%	$102.2361	$102.24	$102.25	$102.20
Purchase #2	$82.54	7.862%	$89.0293	$89.03	$89.05	$89.00
Purchase #3	$11.91	6.168%	$12.6446	$12.64	$12.65	$12.60
Purchase #4	$69.31	13.665%	$78.7812	$78.78	$78.80	$78.80
Purchase #5	$197.89	10.307%	$218.2865	$218.29	$218.30	$218.30
Purchase #6	$79.73	12.500%	$89.6963	$89.70	$89.70	$89.70
Purchase #7	$83.77	5.557%	$88.4251	$88.43	$88.45	$88.40
7 purchase totals =	$614.99		$679.0991	$679.11	$679.20	$679.00