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	$54.99	8.836%	$59.8489	$59.85	$59.85	$59.80
Purchase #2	$178.60	6.576%	$190.3447	$190.34	$190.35	$190.30
Purchase #3	$188.59	8.386%	$204.4052	$204.41	$204.40	$204.40
Purchase #4	$204.72	10.443%	$226.0989	$226.10	$226.10	$226.10
Purchase #5	$75.29	11.186%	$83.7119	$83.71	$83.70	$83.70
Purchase #6	$55.27	13.817%	$62.9067	$62.91	$62.90	$62.90
Purchase #7	$116.27	12.776%	$131.1247	$131.12	$131.10	$131.10
7 purchase totals =	$873.73		$958.4410	$958.44	$958.40	$958.30