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	$25.44	11.306%	$28.3162	$28.32	$28.30	$28.30
Purchase #2	$49.94	9.794%	$54.8311	$54.83	$54.85	$54.80
Purchase #3	$172.82	8.143%	$186.8927	$186.89	$186.90	$186.90
Purchase #4	$11.55	7.426%	$12.4077	$12.41	$12.40	$12.40
Purchase #5	$89.97	6.132%	$95.487	$95.49	$95.50	$95.50
Purchase #6	$203.92	7.727%	$219.6769	$219.68	$219.70	$219.70
Purchase #7	$31.81	6.721%	$33.948	$33.95	$33.95	$33.90
7 purchase totals =	$585.45		$631.5596	$631.57	$631.60	$631.50