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	$139.65	12.267%	$156.7809	$156.78	$156.80	$156.80
Purchase #2	$20.27	11.616%	$22.6246	$22.62	$22.60	$22.60
Purchase #3	$205.86	8.622%	$223.6092	$223.61	$223.60	$223.60
Purchase #4	$45.75	3.617%	$47.4048	$47.40	$47.40	$47.40
Purchase #5	$200.71	11.278%	$223.3461	$223.35	$223.35	$223.30
Purchase #6	$123.77	3.520%	$128.1267	$128.13	$128.15	$128.10
Purchase #7	$142.27	12.145%	$159.5487	$159.55	$159.55	$159.50
7 purchase totals =	$878.28		$961.4410	$961.44	$961.45	$961.30