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	$29.89	4.584%	$31.2602	$31.26	$31.25	$31.30
Purchase #2	$122.42	13.573%	$139.0361	$139.04	$139.05	$139.00
Purchase #3	$170.46	4.618%	$178.3318	$178.33	$178.35	$178.30
Purchase #4	$198.27	5.204%	$208.588	$208.59	$208.60	$208.60
Purchase #5	$107.64	10.403%	$118.8378	$118.84	$118.85	$118.80
Purchase #6	$187.98	5.453%	$198.2305	$198.23	$198.25	$198.20
Purchase #7	$90.85	10.355%	$100.2575	$100.26	$100.25	$100.30
7 purchase totals =	$907.51		$974.5419	$974.55	$974.60	$974.50