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	$249.26	10.445%	$275.2952	$275.30	$275.30	$275.30
Purchase #2	$65.95	13.477%	$74.8381	$74.84	$74.85	$74.80
Purchase #3	$218.81	5.754%	$231.4003	$231.40	$231.40	$231.40
Purchase #4	$102.99	10.821%	$114.1345	$114.13	$114.15	$114.10
Purchase #5	$204.39	9.870%	$224.5633	$224.56	$224.55	$224.60
Purchase #6	$41.93	3.710%	$43.4856	$43.49	$43.50	$43.50
Purchase #7	$39.27	3.389%	$40.6009	$40.60	$40.60	$40.60
7 purchase totals =	$922.60		$1,004.3179	$1,004.32	$1,004.35	$1,004.30