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	$165.63	3.761%	$171.8593	$171.86	$171.85	$171.90
Purchase #2	$75.85	5.850%	$80.2872	$80.29	$80.30	$80.30
Purchase #3	$122.51	4.206%	$127.6628	$127.66	$127.65	$127.70
Purchase #4	$109.52	5.373%	$115.4045	$115.40	$115.40	$115.40
Purchase #5	$117.46	13.397%	$133.1961	$133.20	$133.20	$133.20
Purchase #6	$175.43	8.127%	$189.6872	$189.69	$189.70	$189.70
Purchase #7	$164.77	11.839%	$184.2771	$184.28	$184.30	$184.30
7 purchase totals =	$931.17		$1,002.3742	$1,002.38	$1,002.40	$1,002.50