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	$80.81	3.209%	$83.4032	$83.40	$83.40	$83.40
Purchase #2	$30.71	11.731%	$34.3126	$34.31	$34.30	$34.30
Purchase #3	$247.74	13.182%	$280.3971	$280.40	$280.40	$280.40
Purchase #4	$143.57	4.821%	$150.4915	$150.49	$150.50	$150.50
Purchase #5	$184.47	3.788%	$191.4577	$191.46	$191.45	$191.50
Purchase #6	$129.78	4.350%	$135.4254	$135.43	$135.45	$135.40
Purchase #7	$222.42	5.165%	$233.908	$233.91	$233.90	$233.90
7 purchase totals =	$1,039.50		$1,109.3955	$1,109.40	$1,109.40	$1,109.40