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	$228.30	9.255%	$249.4292	$249.43	$249.45	$249.40
Purchase #2	$37.86	10.454%	$41.8179	$41.82	$41.80	$41.80
Purchase #3	$69.29	11.327%	$77.1385	$77.14	$77.15	$77.10
Purchase #4	$221.49	9.585%	$242.7198	$242.72	$242.70	$242.70
Purchase #5	$141.85	6.263%	$150.7341	$150.73	$150.75	$150.70
Purchase #6	$50.65	5.133%	$53.2499	$53.25	$53.25	$53.20
Purchase #7	$176.95	7.151%	$189.6037	$189.60	$189.60	$189.60
7 purchase totals =	$926.39		$1,004.6931	$1,004.69	$1,004.70	$1,004.50