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	$28.40	13.302%	$32.1778	$32.18	$32.20	$32.20
Purchase #2	$80.92	5.167%	$85.1011	$85.10	$85.10	$85.10
Purchase #3	$130.95	8.762%	$142.4238	$142.42	$142.40	$142.40
Purchase #4	$74.59	11.109%	$82.8762	$82.88	$82.90	$82.90
Purchase #5	$188.85	3.379%	$195.2312	$195.23	$195.25	$195.20
Purchase #6	$137.55	4.872%	$144.2514	$144.25	$144.25	$144.30
Purchase #7	$43.92	13.708%	$49.9406	$49.94	$49.95	$49.90
7 purchase totals =	$685.18		$732.0021	$732.00	$732.05	$732.00