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	$204.83	8.599%	$222.4433	$222.44	$222.45	$222.40
Purchase #2	$69.25	13.215%	$78.4014	$78.40	$78.40	$78.40
Purchase #3	$95.41	8.711%	$103.7212	$103.72	$103.70	$103.70
Purchase #4	$26.47	11.301%	$29.4614	$29.46	$29.45	$29.50
Purchase #5	$181.60	6.398%	$193.2188	$193.22	$193.20	$193.20
Purchase #6	$83.63	8.254%	$90.5328	$90.53	$90.55	$90.50
Purchase #7	$191.89	10.140%	$211.3476	$211.35	$211.35	$211.30
7 purchase totals =	$853.08		$929.1265	$929.12	$929.10	$929.00