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	$18.89	8.238%	$20.4462	$20.45	$20.45	$20.40
Purchase #2	$128.37	11.809%	$143.5292	$143.53	$143.55	$143.50
Purchase #3	$181.56	11.109%	$201.7295	$201.73	$201.75	$201.70
Purchase #4	$14.31	10.447%	$15.805	$15.81	$15.80	$15.80
Purchase #5	$67.27	13.646%	$76.4497	$76.45	$76.45	$76.40
Purchase #6	$157.60	6.633%	$168.0536	$168.05	$168.05	$168.10
Purchase #7	$19.32	10.768%	$21.4004	$21.40	$21.40	$21.40
7 purchase totals =	$587.32		$647.4136	$647.42	$647.45	$647.30