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	$30.88	6.455%	$32.8733	$32.87	$32.85	$32.90
Purchase #2	$207.48	5.755%	$219.4205	$219.42	$219.40	$219.40
Purchase #3	$153.71	5.369%	$161.9627	$161.96	$161.95	$162.00
Purchase #4	$92.84	7.414%	$99.7232	$99.72	$99.70	$99.70
Purchase #5	$25.31	6.834%	$27.0397	$27.04	$27.05	$27.00
Purchase #6	$78.80	13.441%	$89.3915	$89.39	$89.40	$89.40
Purchase #7	$128.27	11.839%	$143.4559	$143.46	$143.45	$143.50
7 purchase totals =	$717.29		$773.8668	$773.86	$773.80	$773.90