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	$29.72	7.358%	$31.9068	$31.91	$31.90	$31.90
Purchase #2	$200.52	12.783%	$226.1525	$226.15	$226.15	$226.20
Purchase #3	$72.72	13.705%	$82.6863	$82.69	$82.70	$82.70
Purchase #4	$104.62	9.385%	$114.4386	$114.44	$114.45	$114.40
Purchase #5	$47.37	4.314%	$49.4135	$49.41	$49.40	$49.40
Purchase #6	$145.46	7.468%	$156.323	$156.32	$156.30	$156.30
Purchase #7	$46.74	11.477%	$52.1043	$52.10	$52.10	$52.10
7 purchase totals =	$647.15		$713.0250	$713.02	$713.00	$713.00