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	$150.56	3.640%	$156.0404	$156.04	$156.05	$156.00
Purchase #2	$158.65	5.522%	$167.4107	$167.41	$167.40	$167.40
Purchase #3	$202.59	6.526%	$215.811	$215.81	$215.80	$215.80
Purchase #4	$121.29	4.832%	$127.1507	$127.15	$127.15	$127.20
Purchase #5	$106.31	9.592%	$116.5073	$116.51	$116.50	$116.50
Purchase #6	$138.48	8.489%	$150.2356	$150.24	$150.25	$150.20
Purchase #7	$181.27	13.813%	$206.3088	$206.31	$206.30	$206.30
7 purchase totals =	$1,059.15		$1,139.4645	$1,139.47	$1,139.45	$1,139.40