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	$28.80	13.815%	$32.7787	$32.78	$32.80	$32.80
Purchase #2	$134.66	5.275%	$141.7633	$141.76	$141.75	$141.80
Purchase #3	$24.70	9.468%	$27.0386	$27.04	$27.05	$27.00
Purchase #4	$114.68	7.295%	$123.0459	$123.05	$123.05	$123.00
Purchase #5	$129.80	12.186%	$145.6174	$145.62	$145.60	$145.60
Purchase #6	$89.92	12.282%	$100.964	$100.96	$100.95	$101.00
Purchase #7	$17.57	5.267%	$18.4954	$18.50	$18.50	$18.50
7 purchase totals =	$540.13		$589.7033	$589.71	$589.70	$589.70