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	$79.70	4.795%	$83.5216	$83.52	$83.50	$83.50
Purchase #2	$233.27	13.227%	$264.1246	$264.12	$264.10	$264.10
Purchase #3	$177.96	3.621%	$184.4039	$184.40	$184.40	$184.40
Purchase #4	$30.73	11.641%	$34.3073	$34.31	$34.30	$34.30
Purchase #5	$248.79	12.776%	$280.5754	$280.58	$280.60	$280.60
Purchase #6	$143.77	11.346%	$160.0821	$160.08	$160.10	$160.10
Purchase #7	$107.56	11.697%	$120.1413	$120.14	$120.15	$120.10
7 purchase totals =	$1,021.78		$1,127.1562	$1,127.15	$1,127.15	$1,127.10