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	$200.75	5.252%	$211.2934	$211.29	$211.30	$211.30
Purchase #2	$81.74	10.583%	$90.3905	$90.39	$90.40	$90.40
Purchase #3	$73.71	11.328%	$82.0599	$82.06	$82.05	$82.10
Purchase #4	$159.49	3.328%	$164.7978	$164.80	$164.80	$164.80
Purchase #5	$145.27	4.492%	$151.7955	$151.80	$151.80	$151.80
Purchase #6	$165.37	11.305%	$184.0651	$184.07	$184.05	$184.10
Purchase #7	$5.87	10.215%	$6.4696	$6.47	$6.45	$6.50
7 purchase totals =	$832.20		$890.8718	$890.88	$890.85	$891.00