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	$9.35	7.119%	$10.0156	$10.02	$10.00	$10.00
Purchase #2	$179.76	5.827%	$190.2346	$190.23	$190.25	$190.20
Purchase #3	$167.36	10.869%	$185.5504	$185.55	$185.55	$185.60
Purchase #4	$28.43	12.404%	$31.9565	$31.96	$31.95	$32.00
Purchase #5	$69.71	11.338%	$77.6137	$77.61	$77.60	$77.60
Purchase #6	$99.71	9.735%	$109.4168	$109.42	$109.40	$109.40
Purchase #7	$189.72	13.485%	$215.3037	$215.30	$215.30	$215.30
7 purchase totals =	$744.04		$820.0913	$820.09	$820.05	$820.10