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	$114.47	12.644%	$128.9436	$128.94	$128.95	$128.90
Purchase #2	$172.82	3.756%	$179.3111	$179.31	$179.30	$179.30
Purchase #3	$101.65	8.151%	$109.9355	$109.94	$109.95	$109.90
Purchase #4	$213.61	9.534%	$233.9756	$233.98	$234.00	$234.00
Purchase #5	$82.43	9.695%	$90.4216	$90.42	$90.40	$90.40
Purchase #6	$62.52	5.133%	$65.7292	$65.73	$65.75	$65.70
Purchase #7	$20.96	3.304%	$21.6525	$21.65	$21.65	$21.70
7 purchase totals =	$768.46		$829.9691	$829.97	$830.00	$829.90