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	$137.76	5.610%	$145.4883	$145.49	$145.50	$145.50
Purchase #2	$99.72	12.619%	$112.3037	$112.30	$112.30	$112.30
Purchase #3	$98.39	10.130%	$108.3569	$108.36	$108.35	$108.40
Purchase #4	$91.43	8.584%	$99.2784	$99.28	$99.30	$99.30
Purchase #5	$81.50	5.794%	$86.2221	$86.22	$86.20	$86.20
Purchase #6	$150.37	5.545%	$158.708	$158.71	$158.70	$158.70
Purchase #7	$162.30	11.790%	$181.4352	$181.44	$181.45	$181.40
7 purchase totals =	$821.47		$891.7926	$891.80	$891.80	$891.80