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	$27.45	6.345%	$29.1917	$29.19	$29.20	$29.20
Purchase #2	$87.86	13.823%	$100.0049	$100.00	$100.00	$100.00
Purchase #3	$139.70	11.813%	$156.2028	$156.20	$156.20	$156.20
Purchase #4	$211.40	9.135%	$230.7114	$230.71	$230.70	$230.70
Purchase #5	$127.50	3.433%	$131.8771	$131.88	$131.90	$131.90
Purchase #6	$158.94	6.282%	$168.9246	$168.92	$168.90	$168.90
Purchase #7	$99.80	3.526%	$103.3189	$103.32	$103.30	$103.30
7 purchase totals =	$852.65		$920.2314	$920.22	$920.20	$920.20