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	$45.98	5.524%	$48.5199	$48.52	$48.50	$48.50
Purchase #2	$250.76	11.477%	$279.5397	$279.54	$279.55	$279.50
Purchase #3	$217.59	4.562%	$227.5165	$227.52	$227.50	$227.50
Purchase #4	$176.60	6.124%	$187.415	$187.42	$187.40	$187.40
Purchase #5	$145.65	7.131%	$156.0363	$156.04	$156.05	$156.00
Purchase #6	$101.49	8.399%	$110.0141	$110.01	$110.00	$110.00
Purchase #7	$31.30	6.292%	$33.2694	$33.27	$33.25	$33.30
7 purchase totals =	$969.37		$1,042.3109	$1,042.32	$1,042.25	$1,042.20