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	$102.95	6.646%	$109.7921	$109.79	$109.80	$109.80
Purchase #2	$77.30	6.341%	$82.2016	$82.20	$82.20	$82.20
Purchase #3	$59.41	11.761%	$66.3972	$66.40	$66.40	$66.40
Purchase #4	$20.61	5.595%	$21.7631	$21.76	$21.75	$21.80
Purchase #5	$16.40	13.703%	$18.6473	$18.65	$18.65	$18.60
Purchase #6	$247.44	6.183%	$262.7392	$262.74	$262.75	$262.70
Purchase #7	$52.89	11.723%	$59.0903	$59.09	$59.10	$59.10
7 purchase totals =	$577.00		$620.6308	$620.63	$620.65	$620.60