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	$36.31	9.516%	$39.7653	$39.77	$39.75	$39.80
Purchase #2	$99.97	9.495%	$109.4622	$109.46	$109.45	$109.50
Purchase #3	$43.73	13.286%	$49.54	$49.54	$49.55	$49.50
Purchase #4	$184.78	13.117%	$209.0176	$209.02	$209.00	$209.00
Purchase #5	$181.66	8.171%	$196.5034	$196.50	$196.50	$196.50
Purchase #6	$27.74	11.254%	$30.8619	$30.86	$30.85	$30.90
Purchase #7	$50.39	3.336%	$52.071	$52.07	$52.05	$52.10
7 purchase totals =	$624.58		$687.2214	$687.22	$687.15	$687.30