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	$52.46	13.168%	$59.3679	$59.37	$59.35	$59.40
Purchase #2	$57.93	7.588%	$62.3257	$62.33	$62.35	$62.30
Purchase #3	$174.30	7.382%	$187.1668	$187.17	$187.15	$187.20
Purchase #4	$145.42	8.815%	$158.2388	$158.24	$158.25	$158.20
Purchase #5	$203.76	5.498%	$214.9627	$214.96	$214.95	$215.00
Purchase #6	$28.67	4.104%	$29.8466	$29.85	$29.85	$29.80
Purchase #7	$55.52	11.107%	$61.6866	$61.69	$61.70	$61.70
7 purchase totals =	$718.06		$773.5951	$773.61	$773.60	$773.60